The invention relates to a dual gas cylinder combined type two-stage engine. The dual gas cylinder combined type two-stage engine comprises an engine body with a combustion chamber. A primary piston is sealed in the combustion chamber in a sliding manner and is connected with a crankshaft through a primary connecting rod. A first gas inlet and a sparking plug are arranged on the combustion chamber. A mixing chamber communicating with the combustion chamber is further arranged in the engine body. A gas release valve is arranged on a channel between the combustion chamber and the mixing chamber. A secondary piston in sealing sliding fit is arranged in the mixing chamber. The secondary piston is hinged to the crankshaft through a secondary connecting rod. A second gas inlet and an exhaust opening are formed in the mixing chamber. The primary piston and the secondary piston alternately move under rotation of the crankshaft. According to the dual gas cylinder combined type two-stage engine, the tail gas exhaust temperature can be greatly reduced, the acting efficiency of the engine body can be improved, the temperature of the engine body can be reduced, energy consumption can be reduced, and the operating cost can be reduced.