Phase selection making technology can greatly reduce transient over voltage and inrush current in the closing operation of circuit breaker, improve endurance of power equipment and stability of electric power system and have been rapidly developed and applied in ultra-high and extra-high voltage system. With its increased application and network operation, phase selection problems occurred frequently such as prebreakdown, overvoltage/inrush current. Phase-controlled circuit breaker is taken as the research object. Aiming at the problems in the process of phase selection and combination, theoretical analysis and experimental verification methods are adopted. The reasons are analyzed by combining the basic theory and principle of phase selection control technology. It is considered to be the fundamental reason to cause making operation in phase selection of phase-controlled circuit breaker that actual closing time t deviates greatly from expected closing time T. The mutual change between anticipated closing time T and active closing time is the fundamental reason to cause phase selection problem.