Abstract: Combined with the engineering practice of coal mine fire prevention and extinguishing engineering with liquid nitrogen, on the basis of analyzing the heat transfer process in the liquid nitrogen transportation pipeline, it introduced and compared two calculation methods of two-phase nitrogen pipeline transportation pressure drop, which included homogeneous model and Lockhart-Martinelli correlation, then it analyzed the influence of wall roughness, dryness of two-phase nitrogen at the outlet of pipeline, pipeline diameter and mass flow speed on the pressure drop. The results showed that homogeneous model was suitable for calculating the pressure drop in the case of smaller dryness and Lockhart-Martinelli correlation could be used to calculate the pressure drop of two-phase nitrogen except the annular flow; the wall roughness greatly affected the pressure drop and the influence became bigger with the pipeline diameter becoming smaller; with dryness of two-phase nitrogen at the outlet of pipeline increasing, the pressure drop increased at first and then decreased, so wrapping the pipeline with insulation materials could reduce the dryness of two-phase nitrogen, thus it decreased the pressure drop.