The invention discloses a power auxiliary system with an internal combustion engine, which comprises the internal combustion engine, a steam turbine, a centrifugal compressor and a waste heat recovery device. The waste heat recovery device is used for converting waste heat generated by the internal combustion engine after fuel is burnt into waste gas energy and converting a liquid working medium into steam by the waste gas energy and heat energy generated by cooling liquid of the internal combustion engine so as to drive the steam turbine and the centrifugal compressor to operate and work; and the centrifugal compressor is used as an auxiliary air suction machine of the steam turbine for guaranteeing the relatively low pressure to be always kept inside the steam turbine to ensure a sufficiently pressure difference between the high pressure end and the low pressure end of the steam turbine so as to ensure that the steam turbine generates higher power. By the mode, according to the power auxiliary system with the internal combustion engine, which is provided by the invention, the heat efficiency of the internal combustion engine can be improved and the oil consumption of the internal combustion engine is reduced, the exhaust emission of the internal combustion engine can also be effectively reduced, the petroleum energy resources are saved, the exhaust emission is reduced and the mechanical efficiency is improved.