Component suppliers of wind turbines must make formal testing routine to ensure the reliability of accessories. At the same time, it is also necessary for prototype assembly testing of wind turbines. The purpose of reliability testing is to find potential problems as early as possible and make the system meet its reliability. Reliability testing should be carried out at multiple levels, especially complex systems should be tested at all levels of components, assembly processes, subsystems and systems. If each component should be tested first, the overall test can be performed after the test is passed, thereby reducing project risks. In the system reliability test, a reliability failure report should be generated after each level test, and then analyzed and corrected, which can improve the level of reliability test. Although this kind of test takes a lot of time and expense, it is worthwhile compared to the long-term downtime due to faults in actual operation and the loss caused by product instability. For offshore wind turbines, this test needs to be strictly implemented.