Preparation method of polyether glycol with stable viscosity and high molecular weight

The invention relates to a preparation method of polyether glycol with stable viscosity and high molecular weight. The invention mainly aims to solve the problems of relatively high product viscosity,unstable product quality and low batch production yield during preparation of polyether glycol with high molecular weight in the prior art, and provides a novel preparation method of polyether glycolwith stable viscosity and high molecular weight. According to a technical scheme in the invention, the preparation method comprises the following steps: uniformly mixing a high-activity amorphous double-metal cyaniding complex catalyst DMC and low-molecular-weight polyether glycol to obtain a material A; continuously adding the material A and propylene oxide (PO) into a reactor I in proportion, and carrying out standing for at least 30 minutes; continuously transferring the polyether glycol in the reactor I into a reactor II, and carrying out standing for at least 30 minutes; and performing continuous discharging so a