Abstract: A new type pressure-relieving device was presented. This device takes the advantages of two kinds of existing pressure-relieving devices, namely the spring direct action type relieving valve and bellows pilot operated type relieving valve. This device is of advantages with high release credibility, good reliability, good tightness, and operation smooth and steady, etc. In order to validate the reliability and credibility of the actual working performance for the presented device, the hot state experiment was performed at 15.5 MPa working pressure. The sealing characteristic curve and the performance characteristic curve of the device were obtained from experiments. The results show that the work performance of pressure-relieving device is good. It provides a new thinking to improve performance of pressure safety system for pressurized water reactor, and the experience of using the device in future is accumulated by performing the validation experiments.