The hydraulic system provides power for the working device of the construction crane, and the correct maintenance of the hydraulic system is very important to improve the working reliability of the crane. Generally speaking, the hydraulic system is usually flushed before it is put into operation. The purpose of flushing is to remove the residual pollutants, metal chips, fiber compounds and iron cores in the system. In the first two hours of work, even if the system is not completely damaged, it will cause a series of failures. Therefore, the cleaning of the system oil circuit should be carried out according to the following steps: clean the oil tank with easy-to-dry cleaning solvent, and then remove the solvent residue with filtered air. Clean all pipes of the system, and in some cases, it is necessary to impregnate pipes and joints. Install an oil filter in the pipeline to protect the oil supply pipeline and pressure pipeline of the valve. Install a flushing plate on the current collector instead of a precision valve, such as an electro-hydraulic servo valve. Check all pipelines for proper size and correct connection. If the system adopts electro-hydraulic servo valve, the author may wish to say a few more words. The flushing plate of the servo valve should make the oil flow from the oil supply pipeline to the oil collector and directly return to the oil tank, so that the oil can be repeatedly circulated to flush the system, allowing the oil to filter out solid particles. During flushing, check the oil filter every 1 ~ 2 hours to prevent the oil filter from being blocked by pollutants. At this time, the bypass should not be opened. If you find that the oil filter is blocked, please change the oil immediately. The flushing cycle is determined by the structure of the system and the pollution degree of the system. If there are no or only a few foreign pollutants in the filter medium of the sample, install a new oil filter, remove the washing plate and install the valve to work. Planned maintenance: establish a systematic regular maintenance system. Suggestions for better maintenance of the hydraulic system are as follows: check and replace the oil filter at most 500 hours or three months. Clean the oil inlet filter of the oil pump regularly. Check whether the hydraulic oil is polluted by acidification or other pollutants, and the smell of the hydraulic oil can roughly tell whether it has deteriorated. Fix the loopholes in the system. Ensure that no foreign matter enters the oil tank from the vent cover of the oil tank, the plug seat of the oil filter, the gasket of the oil return line and other openings of the oil tank.