Provided is a hydraulic system for a mold hydraulic testing machine. The hydraulic system comprises an oil tank, a hydraulic pump, an electric motor connected with the pump shaft of the hydraulic pump, a proportional valve used for controlling the pressure and the flow of hydraulic oil, a valve plate, a plurality of electromagnetic valves arranged on the valve plate for controlling circulating or closing of a hydraulic channel, and a cooler for cooling the hydraulic oil, wherein the oil tank is communicated with the hydraulic pump through a pipeline, the hydraulic pump is communicated with the proportional valve through a pipeline, and the proportional valve is communicated with the valve plate through a pipeline; the valve plate is communicated with an oil cylinder of a tested mold through a pipeline, the valve plate is communicated with the cooler through a pipeline, and the cooler is communicated with the oil tank through a pipeline to form a hydraulic detecting and cooling circuit. The mold hydraulic testing machine which adopts the hydraulic system can conduct testing on the mold during mold assembly and after mold assembly, before mold testing on an injection molding machine and before mold transportation.