The invention relates to a method for producing high-molecular-weight polyether by adopting a micro-channel reactor. The method adopts a micro-reactor, a micro-mixer, a pretreatment kettle, a preheating pipe, a delay pipe, a metering pump A, a metering pump B, an epoxy compound storage tank B, a collection kettle, a neutralization kettle, a desalting device, a post-treatment kettle, a back pressure valve and a pressure gauge. The micro-reactor is provided with a plurality of micro-channels, two micro-reactor feed ports and a micro-reactor discharge port; the micro-reactor, the micro-mixer andthe delay pipe form a micro-reaction unit; the desalting device comprises a post-treatment kettle and a filtering machine; and the pressure gauge is arranged between the micro-mixer and the back pressure valve. The method is advanced and scientific, the micro-reactor system adopted in the method is rapid and uniform in mixing, the over-temperature phenomenon is avoided, side reactions are reduced,low-unsaturation-degree and high-molecular-weight polyether can be continuously produced, direct large-scale production can be achieved, and the method has high safety performance and is suitable forindustrial production.