Abstract: Passive intermodulation (PIM),as an important interference affection in base station and satellite antenna systems was widely recognized.Prediction of the PIM power level is one of difficult points in the PIM studies.Two prediction methods of PIM power level were compared and analyzed.The mathmatical model was set up,and the measurment errors of 3,5,7 order PIM were obtained by the two methods under different output measurement errors and same input voltage through computer simulation.The validities were discussed by comparing our data with the actual measurment data in other relative paper.