By studying relevant regulations, standards and good practices, this paper discusses the typical types of common cause failures (CCFs) and general countermeasures in nuclear power plants, and summarizes the methodology, process and defenses for CCFs analysis of safety ventilation and air-conditioning (VAC) system in nuclear power plants. The typical CCFs are divided into four categories, namely functional dependency, spatial dependencies, inherent dependencies and human-related dependencies, and the corresponding defences are functional isolation, physical isolation, and diversity respectively. Comprehensive CCFs risk analysis of VAC system involves plant fault study, equipment FMECA analysis, PSA analysis, hazards analysis and other fields. For the identified CCF points, The optimal solution can be determined by combining factors which include technology maturity, feasibility, engineering cost, etc., and methods such as equipment diversity, physical isolation and functional isolation can be used to reduce or eliminate CCF points, to achieve as low as reasonably practicable (ALARP) risk of CCFs. The CCFs analysis methodology, process and defences summarized in this paper can provide reference for the CCFs of other nuclear safety supporting and auxiliary systems in nuclear power plants.