The invention discloses a speed changer, a power transmission system and a vehicle. The speed changer comprises a plurality of input shafts, a plurality of output shafts, fixed output gears, an output part, a motor gear, an output part synchronizer and a motor power shaft, wherein the output part is arranged on one of the outputs in an idling mode; the fixed output gears are fixedly arranged on the rest output shafts; the motor gear is fixedly arranged on one of the output shafts; the output part synchronizer is arranged on one of the output shafts and is at least used for connecting with the output part; and the motor power shaft is fixedly provided with a motor power shaft gear which is arranged to be linked with the motor gear. According to the speed changer, transmission modes are enriched, and various work conditions of charging during parking, charging during engine driving and the like can be realized.