Disclosed is an ammonia-hydrogen blended fuel control system based on reactivity regulation. The control system comprises a vehicle-mounted ammonia-hydrogen fuel supply system, an ammonia-hydrogen blended fuel premixed combustion engine and an ECU (Electronic Control Unit). The ECU is used for regulating the air injection amount and pressure value of ammonia fuel and hydrogen waiting to enter the ammonia-hydrogen blended fuel premixed combustion engine. The vehicle-mounted ammonia-hydrogen fuel supply system comprises a low-pressure liquid ammonia supply unit and a vehicle-mounted hydrogen production unit, and is used for providing the prepared low-pressure ammonia fuel and hydrogen for the ammonia-hydrogen blended fuel premixed combustion engine. The ammonia-hydrogen blended fuel premixed combustion engine comprises a turbulent jet ignition device provided with a pre-chamber. An ammonia injector and a first hydrogen injector which face the cylinder head are respectively arranged on the air inlet pipe.