The invention discloses a built-in cooling system of an injection molding machine. The system comprises a working table, wherein an air compressor and a water tank are arranged in the working table, the air compressor is connected with the water tank through a pipeline; a mold is arranged on the working table; the mold is connected with the water tank though a water inlet pipeline and a water outlet pipeline; the water tank is connected with a device cooling water outlet pipeline; and the air compressor is connected with a device cooling water inlet pipeline. According to the built-in cooling system of the injection molding machine, the water tank is arranged in the injection molding machine and the cooling effect is achieved through water in the water tank, the air compressor provides circulating power for cooling water, so that the injection molding machine is small in size, small in occupied space and good in cooling effect.