Variation of brown soil organic phosphorus fractions in different periods after application of outside source of humic acid were studied with Bowman-Cole method.The results indicated that:(1)In every period of cultivation,the structure of organic phosphorus fraction had not changed,still was:moderately liable organic phosphorus>moderately stable organic phosphorus>highly stable organic phosphorus>liable organic phosphorus.(2)The liable organic phosphorus all decreased after application of outside source of humic acid in 30 days cultivation.The liable organic phosphorus increased after application of highest humic acid in 60 and 90 days cultivation.(3)The moderately liable stable organic phosphorus obviously increased in all periods of cultivation after application of outsides source of humic acid,especially fertilizer in highest humic acid increased at most.(4)The moderately stable organic phosphorus decreased after application of outside source of humic acid,especially fertilizer in highest humic acid decreased at most.