Of course, polygraph, like any means of investigation including technical means, has its special functions and limitations. Lie detection can never replace investigation and interrogation. It is not illegal to take a polygraph with the consent of the candidates, perform the necessary procedures, and take a polygraph in strict accordance with the requirements of the polygraph procedure, and it can receive the due results. But the abuse of polygraph will lead to bad consequences. Finding out the case mainly depends on painstaking investigation, investigation and interrogation, and polygraph technology can only be used as an auxiliary investigation means. We should seek truth from facts and correctly understand the function of polygraph technology, that is, we should not completely deny it, nor expect too much from it and exaggerate its function. Recently, the media has blown the lie detector to the gods. The lie detector mythologized by the media gives people a misleading message: with it, no matter how cunning criminals are, they can't escape legal sanctions, and even the most difficult cases will be "solved at once"; With it, the judicial and discipline inspection departments can easily crack major cases and clean up social evils just around the corner. In fact, the polygraph is not omnipotent, and the evidence it "produces" is the same as other scientific evidence, and it is impossible to be 100% correct. The object of polygraph work is a living and thoughtful person, and the instrument detects the psychological change parameters of the examinee. Therefore, the psychological status of the subjects is directly related to the test results.

Practice has proved that pre-test conversation is a very important part of the whole polygraph process. In a sense, the conversation before the exam is more important than the formal exam. Whether the subject can react correctly in the test depends on whether he is in the psychological state needed for lie detection before the test. And this kind of psychological state needs the polygraph examiner to guide and adjust through the pre-test conversation. Test whether the previous conversation is correct.

Whether it goes deep or not directly determines the effect of the test, and even affects the accuracy of the test. Of course, the accuracy of polygraph depends on many factors, such as intelligence level, physical and mental condition, test environment, test conditions and the professional quality of polygraph personnel. It is understood that as one of the countries with the most advanced psychological testing technology, the relevant laws in the United States have very strict requirements for testers, and they must receive formal training for up to six months at the polygraph college. Students must have a bachelor's degree or above and have a professional background in psychology. However, at present, few people in charge of testing cases in China have been trained by psychologists, and few people have received strict relevant training, which greatly reduces the level of psychological testing questions. If the psychology of the offender is not scientifically analyzed, the tester may ask some inaccurate questions, such as "Were you there on the night of the crime?" . Because the subjects may have been asked this question severely many times before, even when they were reprimanded, the memory left after strong stimulation will make the biological curve of the subjects react abnormally even when answering "never been". This misunderstanding is likely to ruin the subject's life. Therefore, at this stage, China's judicial organs are very cautious about the use of polygraph for criminal suspects, and do not decide the case based on the results, let alone allow polygraph to replace reconnaissance and trial work. At present, enterprises and individuals are prohibited from buying and using lie detectors; If the polygraph is forcibly used, it will definitely hurt citizens' personal rights. It is understood that at present, most of the lie detectors used by public security, procuratorial organs, courts and other departments in China are developed and sold by four or five companies or professional institutions, but in fact, many people want to make a fortune. Not only that, some people have not been examined and approved by the public security department, and even tested many times in actual combat. They only tear down a copy of other people's documents and sell them to political and legal organs for use, which highlights the reality that there are thousands of innocent ghosts in a major criminal case that affects people's lives.