With the increase of carrier power

the development trend of sophisticated communication equipment

the inherent non-linearity of passive components will cause serious Passive Inter-Mmodulation（PIM）interference

where the resulting impact can not be ignored.In view of this phenomenon

the microwave rectangular waveguide is taken as the research object

considering the main mechanism of PIM:quantum tunneling effect and hot electron emission effect.Based on the contact model of the waveguide flange Metal-Metal（MM）

a method of calculating the PIM power is proposed.The two non-linear effects are represented by the I-Vcharacteristics of the tunneling resistor Rnlc

using harmonic balance simulation and Matlab software for AC simulation.The non-linear current flowing through the tunneling resistor and the voltage drop at both ends and the PIM power in the waveguide connection are analyzed and calculated.The results show that the calculated PIM power varies with the contact pressure.The value of PIM power drops significantly at first with the increase of pressure.Then the value of PIM power declines slowly when further increasing the pressure and reaches a balanced state finally.