Controllable pitch propeller is widely used as the main ship propulsion with hydraulic systems as power source, but the hydraulic systems with complex structure are always in harsh environment. In order to obtain a more reliable operation in propellers whole life cycle, a reliability research of the hydraulic system is carried out. Based on detailed description of the function and principle of the main controlling hydraulic system, a complex seriesparallel reliability model was established. Then the reliability was predicted from unit to system with the synthetic “failure rate prediction method”, “score estimation method” and “component counting method”, and a FMECA focusing on criticality analysis on some representative units was carried out by using quantitative criticality matrix. The failure rate and the reliability curve of the system and each unit were gotten, as well as the criticality of main units and their failure modes. The results show that this integrated prediction approach is more suitable to apply to systems containing some nonelectronic components whose data is difficult to collect, and some units, such as sequence valves, shuttle valves and relief valves have greater impact on system reliability. It provides a theoretical reference and the direction of improvement for hydraulic system reliability design.