For passive inter-modulation interference of microwave and RF communication system, the non-linear principal mechanisms due to electron tunnelling of metal oxide are analysed and discussed firstly. Mathematical model of the third order PIMP of Al - Al2O3-Al in antenna is constructed. Based on the results of the third order PIMP, the fifth order PIMP is calculated by using power series, and the comparison among the PIMPs produced by different alumina is done. Numerical and measure results indicate that oxide's PIMP power level increases with the increase of input power, and increases with the increase of oxide's thickness.