Abstract: In the process of pigging in natural gas pipeline, it is necessary to utilize the precise and reliable technical means for pig tracking and locating in order to determine the time of pig arrival at points along the pipeline and define the time of start-up for pig collection based on pig position. On the basis of thermodynamics and state equation, coefficients in continuity equation, motion equation and energy equation are expressed as functions of pressure and temperature, and discretized in first-order finite difference format. The equation set is solved to obtain the distributions of pressure and temperature, hence realizing the precise location of pig within gas pipeline. From pig locating practice in a natural gas transmission branch in central China, it is proved that the method is helpful to enhance the accuracy in emulation calculation of natural gas pipeline and the actual engineering requirement can be satisfied.