Provided is a method for preparing a defect-free DDR molecular sieve membrane. Sigma-1 molecular sieve is used as an inducing seed crystal to prepare and obtain a continuous and compact DDR molecular sieve membrane on the surface of a porous ceramic support. An ozone atmosphere or an external field assisted technology is used to remove a template in the pores of the molecular sieve membrane at a low temperature. The invention avoids the formation of intercrystal defects and cracks, an activated DDR molecular sieve membrane has a good selectivity for separating CO2, and the membrane preparation time is significantly reduced.