The invention discloses a rectifier module dormancy control method for a substation DC system. The dormancy control method comprises the following steps: detecting the charging state of a storage battery module; when the charging state of the storage battery module is a floating-charge state, determining the dormancy quantity of each group of rectifier modules according to the wiring mode, the lowest operation quantity and a DC output value of each group of rectifier modules; carrying out alternate dormancy on each group of rectifier modules according to the determined quantity; and controlling the rectifier modules to exit dormancy when the floating-charge state is exited or disturbed. According to the substation DC system and the dormancy control method therefor disclosed by the invention, a storage battery achieves alternate dormancy control on the rectifier modules only in the floating-charge state, and the rectifier modules exit dormancy when the floating-charge state is exited or disturbed, so that the requirements of safe power supply are ensured; the quantity of the dormant rectifier modules is determined according to the load rate obtained by DC output value conversion; and the load rate of the rectifier modules is improved.