Ticagrelor, which is a small molecule anti-clotting drug by oral with high selectivity，is platelet activity without the metabolic activation. However, (1 R, 2 S)-2- (3, 4-difluorophenyl)cyclopropanamine is an important intermediate of ticagrelor. The synthetic conditions of the key-step of Corey-Chaykovsky Asymmetric Cyclopropanation reaction were improved based on the reference. The best condition is that: L-menthol as chiral auxiliary agents ; trimethylsulfonium iodide as sulfur-ylide reagent; DMSO: THF = 4: 1 as reaction solvent; reaction temperature was 10 ℃; 10 % CuI as reaction catalyst; the yield is 60.5 %. Based on the reaction, the total yield of the five steps was 20%.