The direct drive pumpcontrolled servo hydraulic system using AC servo motor and displacement pump has advantages of energysaving, high efficiency and reliabilityetc. The technology was used to reform a traditional horizontal cold chamber die casting machine to save energy. The energy simulation model of the reformed die casting machine was built and the energy simulations and experiments were performed. The results show that the reformed die casting machine can save energy for more than 45% and the productivity can be improved by 5%. By analyzing the saving mechanism,the main reasons for saving energy were concluded that the direct drive pumpcontrolled servo hydraulic system can match between the energy and the load actively to fit the requirements of the changing speed and pressure of executing agency, and can cut down the inevitable throttle loss and overflow loss. The main reason for improving the production efficiency is to accelerate the accumulators speed during the liquidfilled and the idle travel to reduce the working cycle.