The invention belongs to the technical field of caterpillars and particularly relates to hybrid power transmission. A series-parallel connection hybrid power transmission device of a caterpillar comprises a front transmission part, a left side driving part, a left side output speed changing mechanism, a right side driving part, a right side output speed changing mechanism, a middle power coupling mechanism and a sell. According to the series-parallel connection hybrid power transmission device of the caterpillar, in view of motor power using, a straight-driving and steering power coupled double-motor-driving series hybrid power mode has the advantages that the structure is simple, double-current zero-differential-type steering motors and steering zero shafts can be omitted, and reducing of the longitudinal space of the transmission device is facilitated; through the middle power coupling mechanism, efficient transmission of steering reflux power can be achieved, and the technical requirements of the motors are effectively lowered; and through the middle power coupling mechanism, a path of engine power is introduced, during high speed or a stable driving working condition, a parallel connection hybrid power working condition is achieved, the two driving motors can still be used as steering motors to be responsible for steering of the caterpillar.