The invention provides an external internal combustion engine, and relates to the technical field of engines. The external internal combustion engine comprises an air compressor, a motor main body, aheat exchanger and a combustion chamber; the air compressor, the heat exchanger and the combustion chamber communicate in sequence so that the air compressor can enable the air to pass through the heat exchanger and then input the air into the combustion chamber for combustion supporting; the combustion chamber is connected with the motor main body so that expanding gas generated by the combustionchamber can enter the motor main body; the motor main body is used for converting pressure energy of the expanding gas into mechanical energy to be output outwards; the motor main body is connected with the heat exchanger and used for conveying high-temperature expanding gas to the heat exchanger; and the heat exchanger is used for transmitting heat of the high-temperature expanding gas to the air which is output from the air compressor and used for combustion supporting. The heat exchanger recycles and transmits the heat of the high-temperature expanding gas to the air which is output from the air compressor and used for combustion supporting, and the heat utilization rate is increased.