Pulse code mainly includes four kinds of codes such as repetition frequency code, cycle code, pulse code modulation (PCM) code and pseudo-random code, and among which PCM code is the most widely used. PCM code with variable code bit and basic frequency of 1~12 bits and 5~50 Hz is researched. Characteristics and generation principles of PCM code are analyzed. Based on the design of actual hardware and software, implement methods are discussed. Output results of different PCM codes are given finally.