Abstract: In order to evaluate the antielectromagnetic interference capacity of a communication system objectively, an electromagnetic interference experimental method based on symbol error rate (SER) is brought, and then the coupling law of different interference signals is confirmed; the interference mechanism is also analyzed. The results indicate that, for same frequency interference, the SER increases gradually at the first 2 dBm, the later 1 dBm, SER increases fast until 0.47, and the interference power is proportion to the transmitting power. The microphone appears vague when the SER gets 10^-2 level, and the display screen crashes when the SER is 0.47. Signals deviation within transmitting frequency 2 MHz are easy to disturb the communication system. The strong out-band signals will reduce the communication system susceptibility, and the required disturb power is proportional to the frequency deviation extent. When the intermodulation signals vary synchronously, the power is proportional to the transmitting power, otherwise the power fit the equation of frequency. Spread spectrum or RS encoding will enhance the restrain effect of little same frequency signals, for nearby frequency interference, spread spectrum will make the system easy to be disturbed, and the range of interference power is enlarged.