The present invention discloses a synthesis method of lactide by confinement effect catalysis of crystalline porous polymer material, wherein the method comprising: (I) synthesis of catalyst; (II) synthesis of lactide by confinement effect catalysis; and (III) purification of lactide. In the present invention, a yield of L-lactide by catalysis of L-lactic acid by crystalline polymers is as high as 85.6%, which is 10% higher than the yield of lactide by H-β molecular sieve reported in documents currently available; it is easy to prepare the crystalline porous polymer material catalyst, which is environmental friendly, has a high yield and is recyclable, for consecutive 7 times the catalysis yield is maintained to be higher than 70%, and catalysis yield conservation rate is far higher than catalysis effects of catalysts reported in documents currently available.