The invention provides a self-contained power supply system for a crane, mainly comprising a crane body which comprises a lifting device used for lifting a box body. The self-contained power supply system is characterized in that a box body descending generating device is arranged on the lifting device, and is connected with a charging module; the charging module is connected with a storage module used for storing electric energy; the storage module is connected with an inversion module used for supplying power to the external; and the charging module, the storage module and the inversion module are connected with a PLC control module. By adding the system on the crane, the energy generated by the descending of the box body is fully utilized and is converted to the electric energy to be stored, and the electric energy is applied to an electricity user such as an illuminator, an air conditioning, a telephone and the like, therefore, an engine of the crane is started only when the lifting device is used for running; and when the lifting device does not work, the engine can be closed, thereby the oil consumption is saved, and the environmental pollution is also lightened at the same time.