The present invention discloses digital completely isolated myoelectric signal amplifying and noise reducing method and device. The acquired myoelectric signal is processed through amplifying, A/D conversion, low-pass filtering, adaptive wave trapping treatment and isolating to obtain the amplified and noise reduced digital signal. The device for myoelectric signal amplifying and noise reducing includes a bioelectric signal pick-up, a digital signal processor, a digital isolating photocoupler, and a digital output interface circuit. The present invention has the advantages of high safety, highS/N ratio, low power consumption, low cost, easy taking, etc.