The invention relates to a plug-in hybrid driving device based on a mechanical automatic transmission, which belongs to a power driving device of walking machinery. The device comprises an engine, two motors, a two-gear mechanical automatic transmission, a main speed reducer and a differential mechanism, wherein the two-gear mechanical automatic transmission is composed of a mesh gear pair formed by gears of A, B, C, D, H, I, E and F, synchronizers of T and Q and shafts of M, N and O. Model switch of fuel power source driving, electric power source driving or hybrid source driving can be achieved by controlling the synchronizers of T and Q. The plug-in hybrid driving device has the advantages of being capable of effectively using efficient maneuvering areas of the engine and the motors, various in running models, capable of achieving driving synchronous speed regulation and unpowered interrupt control during gear shift, simple and compact in structure, small in axial size and suitable for front-engine front-driving arrangement form.