The invention discloses a preparation method of rare earth-doped double metal cyanide catalyst and a method for preparing low molecular weight poly (carbonic ester-ether) glycol by using the catalyst to catalyze the copolymerization of carbon dioxide and epoxy compounds. The preparation method of poly (carbonic ester-ether) glycol comprises the following steps: using rare earth-doped double metalcyanide based on Zn3[Co(CN)6]2 as a catalyst, and letting carbon dioxide and epoxy compounds be subject to polymerization in the presence of chain transferring agent to obtain the poly(carbonic ester-ether) glycol. According to the invention, compared with the prior art, the rare earth-doped double metal cyanide based on Zn3[Co(CN)6]2 used herein efficiently catalyzes the copolymerization of carbon dioxide and epoxy compounds under the effect of chain transferring agent; and compared with double metal cyanide without doping, the rare earth-doped double metal cyanide based on Zn3[Co(CN)6]2 used herein has higher catalytic activity and better product selectivity.