Abstract: When buried hot oil pipeline experiences any change in transmission process, e. g. reverse pumping, shut-down, start-up, etc., the thermal equilibrium is destoried between the oil in pipeline and the surrounding soil, and the oil temperature and soil temperature redistribute. As a result, in order to study this non-steady thermal process, non-steady temperature field has to be analysed. Using the method of confor-mal transformation in bipolar coordinates, the semi-infinitely large temperature field of the soil is transformed to a finite field, and the method is introduced for calculating the non-steady thermal process for hot oil pipeline. Verifications are made, using this calculation method, based on the experimental data measured during reverse pumping in Hua-Ge Line and Zhong-Luo Looping Line. The numerical caculation is proved quite identical with the actual measured results, and this calculation method is considered applicable to the simulation of non-steady thermal processes for hot oil pipelines such as shut-down, start-up, reverse pumping, etc.