The invention discloses a method for increasing hybrid direct-current (DC) rectifier side power in an alternating-current fault period. LCC (line commutation converter) in a rectifier station is controlled by constant DC current and MMC (modular multilevel voltage source converter) in an inversion station is controlled by constant DC voltage; an alternating-current (AC) voltage detection module is configured to the LCC in the rectifier station and a maximum modulation ratio module is configured to the MMC in the inversion station. When AC voltage detected by the alternating-current voltage detection module is lower than a set value, the maximum modulation ratio module of the MMC is enabled and the control mode of the MMC is controlled from the constant DC voltage to the maximum modulation ratio. The method has the beneficial effects that the MMC is controlled by the maximum modulation ratio when the hybrid direct-current power transmission system presents the AC fault on the rectifier side, and DC transmission power can be effectively increased.