The invention discloses a redundancy decision control method based on double buses, and the method comprises the following steps that S1, one of the spacecraft control units A, B and C is taken as anRT terminal, receives a bus message sent by an MIL-STD-1553B bus transmission after the data is verified to be valid, and transmits a bus message to the other two control units via a CAN bus; S2, oneof the spacecraft control units A, B, and C receives the bus messages sent by the other two control units, and verifies the validity of command data; S3: one of the spacecraft control units A, B and Cperforms the two-out-of-three output of the received MIL-STD-1553B bus message and the bus message forwarded by the other two control units through combining with a heartbeat signal captured by the control unit, so as to cope with known one-degree and two-degree faults. The method uses two mature bus technologies of MIL-STD-1553B and CAN to effectively ensure real-time and highly reliable transmission of bus messages, effectively solves single-point faults of hardware, improves the reliability and security of the system, gives consideration to the balance reliability and economic performance,and has good versatility and scalability.