The invention relates to a thermodynamic circulating system which is applicable to the recycling of waste heat of a vehicle engine. The thermodynamic circulating system is a coupling of low-temperature Kalina cycle used for recycling the waste heat of the cooling water of the engine and high-temperature organic Rankine cycle used for recycling the waste heat of the exhaust of the engine and the waste heat of the lubricating oil, and comprises an exhaust heat exchanger, an expansion machine, a heat exchanger, a pump, a lubricating oil heat exchanger, a lubricating oil circulating pump, a cooling water heat exchanger, a cooling water circulating pump, a heat regenerator, a throttle valve, a separator, the expansion machine, a low-pressure condenser and a pump. The system can overcome the defects that the utilization ratio of the waste heat is not high in the traditional utilization method of the waste heat of the engine, thus obviously improving the recycling efficiency of the waste heat of the vehicle engine.