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%　H2　efficiency　and　477.4　gPO·kgcat-1·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　H2　and　O2　is　the　key　to　initiate　C3H6　epoxidation.　The　general　rules　of　catalytic　mechanism　under　different　size　of　Au　clusters　are　also　analyzed.　©　2023　Elsevier　B.V.