Propylene　oxide　(PO)　is　an　important　intermediate　chemical　and　is　widely　used　in　chemical,　pharmaceutical,　food,　light　industry　and　other　industries.　In　industry,　PO　is　produced　via　multiple　reaction　steps　in　the　liquid　phase,　using　hazardous　chlorine　or　costly　organic　hydroperoxides　as　oxidants.　Considering　the　inherent　defects　of　the　traditional　processes　-　the　chlorohydrin　and　hydroperoxide　process,　a　new　production　technology　that　propylene　oxide　production　via　hydrogen　peroxide　(HPPO)　has　been　developed,　but　many　problems　such　as　the　catalyst　mass　transfer　limitation,　the　catalyst　deactivation　and　regeneration,　and　the　need　of　a　dedicated　hydrogen　peroxide　production　plant　are　encountered.　So,　a　more　attractive　method　for　PO　production　with　molecular　oxygen　by　gas-phase　is　discussed　in　this　paper.　The　most　important　new　developments　for　the　production　of　propylene　oxide　discussed　in　this　paper　are　concentrated　on　the　supported　gold,　silver,　copper,　vanadium,　molten　salt　catalysts　and　other　catalysts　that　used　molecular　oxygen　as　the　oxygen　source.　At　the　same　time,　the　mechanism　involved　in　the　propylene　epoxidation　such　as　the　Ti　active　sites　mechanism　in　Au/Ti　catalysts,　the　OMMP　(OMMP　refers　to　a　ring　made　up　of　one　oxygen　atom,　two　metal　atoms　and　a　propylene　unit)　intermediate　mechanism　in　silver　and　copper　catalysts　and　the　radical　mechanism　in　silver　and　other　metal　oxide　catalysts　are　also　mentioned　in　this　paper.