The invention discloses a waste heat recovery system and a recovery method for an LNG (Liquefied Natural Gas) automobile engine, which aim to solve the technical problem how to reasonably use heat dispersed by automobile exhaust and engine coolant, and additionally, the automobile fuel economy is effectively increased by using LNG fuel cold energy. The waste heat recovery system comprises an organic Rankine cycle system and an LNG fuel cold energy using and heating system, wherein the organic Rankine cycle system is used for recycling waste heat of engine exhaust and coolant, the organic Rankine cycle system comprises a conduction oil circulation loop and an organic working medium circulation loop, the conduction oil circulation loop comprises an exhaust and conduction oil heat exchanger, a conduction oil circulation pump and an evaporator, a conduction oil outlet of the evaporator is connected with a conduction oil inlet of the exhaust and conduction oil heat exchanger by virtue of the conduction oil circulation pump, and a conduction oil outlet is connected with a conduction oil inlet of the evaporator. According to the waste heat recovery system, the heat dispersed by the automobile exhaust and coolant is reasonably used, so that the engine waste heat is recycled, and additionally, the LNG cold energy is fully used.