A garden tool power system comprises a motor, a reducer and a transmission shaft. The motor transmits the power to the transmission shaft through the reducer to drive wheels on the transmission shaft. The reducer comprises a pinion connected to an output end of the motor and a gear engaged with the pinion. The transmission shaft includes left and right shafts connected with each other through a connecting shaft. The gear mounted on the connecting shaft has at least two guiding rods transversely located thereon and two centrifugal blocks located between the guiding rods. Each guiding rod has a spring surrounded therearound and each spring located between two centrifugal blocks has two opposite ends respectively abutted against the corresponding portions of the centrifugal blocks. A fixing sleeve provided on the periphery of the centrifugal blocks is mounted on the transmission shaft and has buckle structures matching with the centrifugal blocks.