The invention provides a PWM wave based multi-channel 4-20 mA control command converting system. The system includes a controller unit (1), an electric level converting unit (2), an isolation conversion unit (3), a low-pass filtering unit (4), a 4-20 mA voltage/current converting unit (5), a current signal transmission cable (6) and a load interface unit (7) connected in sequence. The system is applied as a CPU into an ARM in an embedded system widely with high performance and at a low cost, multi-channel PWM wave voltage signals of required (fixed) frequency and adjustable duty ratio are generated from multi-channel PWM waveforms of TIM of the ARM and are converted to multi-channel 4-20 mA current output signals. The anti-interference capability is improved and multi-channel long-distance transmission is realized. Besides, the system is high in control precision, stable in performance and reliable in operation.