Abstract: The pressure relief system is the key safety guarantee for oil-gas station. Under accident conditions, the high pressure medium must be quickly relieved. The material of vent line is mainly determined by the pipeline temperature during relief. It is necessary to discuss the low temperature condition of the vent medium and vent line, to ensure the rationality and economy of the material selection. In this paper, based on the over-pressure relief and emergency relief process, the influence on the vent line temperature during relief was analyzed in combination with the basic law of engineering thermodynamics, and the low temperature rule of vent line was discussed and simulated with OLGA software. The results showed that the vent line temperature would be close to the relief medium temperature during over-pressure relief, but there would be significant temperature difference under emergency relief. The storage gas and vent line thermal capacity may have an inhibitory effect on the low temperature under emergency relief, and the dynamic simulation can provide technical support on the rational material selection and cost reduction of vent line. The study result will provide reference for fine design of vent line in the gathering station.