The invention relates to a method for sharing channels, comprising the following steps of: A. distributing an idle registration channel for a cognitive user; B. detecting whether an authorized user appears or not, if the authorized user appears, distributing the registration channel for the authorized user, and measuring an interference temperature threshold for ensuring that the authorized user normally uses the registration channel, acquiring the maximum available power of the cognitive user according to the interference temperature threshold, and if the authorized user does not appear, continue to detecting; and C. calculating whether the cognitive user can carry out data transmission or not by using the maximum available power, if so, regulating the transmitting power of the cognitiveuser, and if not, switching the cognitive user to the idle channel. Moreover, the invention also relates to a system for sharing channels. The method and the system for sharing channels judge whetherthe cognitive user can carry out data transmission or not by using the maximum available power to control the action of the cognitive user, which greatly reduces the frequency spectrum switching efficiency, improves the frequency spectrum use ratio and network performance and meanwhile also improves the effective data transfer rate.