Abstract: During the period while medium transported by pipelines, heat propagation is inevitably due to temperature difference between inner pipeline and ambient temperature, and temperature difference distributed along the pipeline will varies. Through introducing length concept of temperature attenuation and based on a calculation method of transition section length at rectangular distribution of temperature difference along the pipeline, the article puts forward an integral equivalent method for calculation of transition section length of neritic buried pipe in pipe line while temperature difference is varying along the pipeline. According to the formula given, analyzes the effect of temperature attenuation length on transition section length and the effect of other coefficients on the transition section lengths given through two calculation methods. It is shown by relative example that the result of value analysis and theoretical analysis are identical, which provides design basis for the transition section of buried pipe in pipe structure in pipeline engineering.