The invention relates to a cold energy and waste heat comprehensive utilization system for a liquefied natural gas (LNG) transport ship. The cold energy and waste heat comprehensive utilization system comprises a high-pressure pump, a first heat exchanger, a second heat exchanger, a third heat exchanger, a first expansion work unit and a second expansion work unit. The first heat exchanger and the second heat exchanger are sequentially connected with an outlet pipeline of the high-pressure pump. The first expansion work unit and the second expansion work unit are connected with an outlet pipeline of the second heat exchanger in parallel. According to the cold energy and waste heat comprehensive utilization system, LNG cold energy, turbine waste steam and boiler exhaust smoke waste heat are used for vaporizing liquid-state LNG to drive an expansion turbine motor to work, and a fan on a boiler is directly driven, so that not only are the LNG cold energy, the turbine waste steam and the boiler exhaust smoke waste heat used fully and comprehensively, but also a large amount of electric energy is saved. Therefore the operating cost of the ship is reduced, and the cold energy and waste heat comprehensive utilization system has very good economic efficiency and environment-friendly performance.