The mixed power drive unit based on double planet ranks has one front planet rank and one rear planet rank. The front planet rank has a sun wheel P, a ring gear S, a planet carrier and a planet gear V; and the rear planet rank has a sun wheel Q, a ring gear T and a planet gear U. The mixed power drive unit has the connection of sun wheels P and Q, connection of front planet carrier and ring gear T, the connection of the internal combustion engine through two clutches separately to ring gear and the planet carrier, the connection of sun gear P and a motor, the connection of the planet carrier and gear H, the connection of sun gear Q and the motor, the connection of sun gears P and Q, the mesh of gear H to gear G, the connection of gear G and the output, the braking of brake C on ring gear S, and the braking of brake E on ring gear T. The present invention has the advantages of compact structure and less transmitting parts, stepless speed change function, etc.