The invention relates to a secondary user access method for maximization of capacity of a dynamic spectrum sharing system, in particular to a secondary user access method which can maximize the capacity of a dynamic spectrum sharing system. In the method, a secondary user selects a channel with the highest transmission power for access during each working cycle of each secondary user, the channel can be known according to a Shannon formula, and each secondary user can obtain the maximum capacity available at present during each working cycle. Therefore, each secondary user can obtain the maximum average capacity in the whole communication period, and the sum of the average capacities of all secondary users can be the maximum, thereby realizing the maximization of the average capacity of the dynamic spectrum sharing system.