The utility model relates to a primary step-down station power system for a 1,000kV ultrahigh voltage substation. The system comprises a #1 station operating transformer, a #0 station operating transformer and a #2 station operating transformer, wherein the #1 and #2 station operating transformers (in leading connection with the low-voltage sides of a #1 main transformer and a #2 main transformer respectively) adopt a 110/0.4kV oil immersed on-load voltage regulating transformer; each station operating transformer is connected to operating generatrixes of sections I and II of a 380/220V station cabinet respectively; a #0 station standby transformer (in leading connection with an external 35kV power supply of the substation) adopts a 35/0.4kV oil immersed on-load voltage regulating transformer; circuit breakers are arranged between the #0 station standby transformer and the operating generatrixes of the sections I and II; and a tie switch is turned off during normal running, and is automatically switched when the station operating transformers are powered off to realize the station power supply of the station standby transformer. The primary step-down station power system has the advantages of high reliability, small voltage fluctuation, investment cost saving, optimization of a building area, and the like, and a gap in the industry is filled.