The invention discloses a multi-gear series-parallel type hybrid power system. The system is composed of an engine, an input shaft, a planetary gear train, a first motor, a second motor, an inverter, a power battery, locking devices, a first gear, a second gear, a third gear, a fourth gear, a fifth gear and clutches. The planetary gear train comprises a front-row sun gear, a front-row planet gear, a front-row gear ring, a planet carrier, a rear-row planet gear and a rear-row gear ring; the locking devices comprise a first locking device and a second locking device; the clutches comprise a first clutch and a second clutch. The hybrid power system is large in number of working modes, wherein the pure electric mode is used more, so that the system is applicable to a plug-in hybrid power vehicle as well; by means of the system, when a vehicle is driven at a high speed, the mechanical path is adopted for transmitting the power instead of using the electric path, the transmission efficiency in the high-speed traveling process of the vehicle is raised, meanwhile, the revolving speed requirement for the second motor can be reduced, and the miniaturization of the second motor is facilitated.