The　epoxidation　of　propylene　(C3H6)　over　TS-1　molecular　sieve　supported　with　nano-Au　clusters　by　deposition-precipitation　(DP)　method　has　always　been　the　focus　of　the　catalytic　field.　A　quantity　of　atomically　dispersed　Au　clusters　can　be　synthesized　induced　by　NH3　as　an　assistant　in　the　DP　system.　These　smaller　Au　clusters　show　14.3%　C3H6　conversion,　91.7%　propylene　oxide　(PO)　selectivity,　10.6%　H-2　efficiency　and　477.4　gPO　center　dot　kg(cat)(-1)center　dot　h(-1)　PO　productivity　in　the　epoxidation　reaction　of　C3H6.　The　interaction　between　NH3　and　[AuCl4](-)　in　aqueous　solution　is　analyzed　by　means　of　experiments　and　Density　Functional　Theory　(DFT),　and　it　is　concluded　that　at　least　2　times　of　NH3　is　needed　to　make　Au　precipitate　completely.　Similarly,　the　mechanism　of　C3H6　epoxidation　catalyzed　by　Aun　(n　=　2,　3,　4)　clusters　in　coordination　with　Ti　sites　is　calculated　with　the　help　of　DFT.　It　is　believed　that　the　in-situ　formation　of　Ti-OOH　structure　at　Ti　sites　through　H-2　and　O-2　is　the　key　to　initiate　C3H6　epoxidation.　The　general　rules　of　catalytic　mechanism　under　different　size　of　Au　clusters　are　also　analyzed.