The main job of the internal auditor is to audit the quality system of the unit, that is, the so-called first-party audit, and the internal auditor often acts as the second-party audit of the subcontractor's quality system.

ISO internal auditor refers to a qualification that is trained according to ISO standards and passed the examination to obtain the internal quality management system audit. Generally, training and assessment are conducted by institutions with ISO-related system consulting qualifications recognized by CNCA, and only those who pass the assessment can take up their posts. It is only applicable to the internal audit of enterprises (units), familiar with the operation process and management responsibilities and authority of enterprises, competent as the basic means and requirements of quality management system for self-improvement and self-management of enterprises, responsible for internal management review, leak detection, supervision and proposing rectification plans.