In communication systems, nonliner circuit was widly used because it could tranform frequency. But nonliner circuit could not analyzed by superposition theorem, it need to be analyzed by switching function method, timevaried circuit analysis method, and ring circuit analysis method. It is difficult to be analyzed by analytical method, and it is often more difficult to be understood. With the help of Multisim 10.0 circuit simulation software, the nonliner circuit can be analyzed from input wave and output wave and spectrum transform. The analysis of the circuit based on Multisim 10.0 is simple and it is also easy to be understood.