Abstract: In order to study the multiphase flow and heat transfer laws of restart-up process for deep water oil and gas pipelines and combined with heat transfer and multi-phase flow theory, this paper establishes the mathematical model for the restart-up process of deep water pipelines, and provides definite conditions and solution for the model in combination of heat transfer and multiphase theory. With this model, it simulates the change laws of temperature and pressure parameters in the restart-up process of deep water pipelines. Based on this, it carries out a prediction on generations of hydrate and an analysis on parameter sensitivity. Research results show that start-up flowrate, thermal conductivity and thickness of insulating layer can improve the temperature distribution of fluid in the pipeline greatly, and the bigger the start-up flowrate is, the smaller the thermal conductivity is; the bigger the thickness and the higher temperature of fluid in the pipeline are, the less the risk of generation of hydrate is. The research conclusions can provide a guideline to safe operation of restart-up deep water oil and water pipelines.