The invention discloses an energy recovery system of an engine. The energy recovery system comprises a turbocharger and an auxiliary supercharging device which is connected with the turbocharger and used for supplying driving power to the turbocharger. The auxiliary supercharging device is provided with an energy accumulator. According to the energy recovery system of the engine, the auxiliary supercharging device is arranged, and the heat, which is the largest energy of the engine, of the engine is fully utilized and is reused in power recycling of the engine. Accordingly, the thermal efficiency of the engine can be improved to a great extent, and the fuel economy of the engine can also be improved.