The aircraft shape could be changed by external equipment, thus the stealth performance could be also influenced. In order to study the variation trend and law of electromagnetic scattering characteristics with different angles and frequency, based on the electromagnetic models of aircraft with and without external equipment, the RCS curves of different frequencies and different pitch angles were simulated by the Physical Optics method. And RCS curves’ distribution characteristics and pitch angle characteristics of the two models were analyzed. The results showed that, in the angle domain on nose direction, the arithmetic mean values of the model without external store in different pitch angles appeared "W" type distribution, and the model with external store appeared inverted "V" distribution. The definition of RCS relative increment was proposed to analyze the influence of external equipment. The relative increments appeared "W" type distribution in angular domain on nose direction, and their values were about 10～25 dB. And the circumferential distribution of relative increments appeared oscillation, and the values were about 7 ~ 17 dB.