A field plot experiment with five P application rates in 4 replications was conducted on the Percogenic paddy soil in the Taihu Lake Region (TLR) under wheat-rice rotation in the year 2001 to 2002, in order to estimate the total phosphorus (TP) lost via drainage flow in wheat season and runoff flow in rice season and to figure out various parts of P loaded by both runoff and drainage flows. Results indicated that the highest P lost via runoff and drainage flow was of 0.75 kg hm^-2, which is less than 0.1% of P applied. However, the concentration of dissolved P in both runoff and drainage flow were higher than 0.02 mg L^-1 (the threshold concentration of P for inland water eutrophication). The result suggested that continuous P application with rate higher than the P demand by crops, certainly increase the risk of water eutrophication. Total P loaded by runoff and drainage flow can be partitioned as part iculate P (PP), representing more than 60% of the TP, and dissolved phosphorus (DP), less than 40%. Among them dissolved organic phosphorus (DOP) was 52.0%~76.2% in all treatments except for the highest P rate applied. Therefore, the amount and the contribution of DP in the runoff and drainage flow have been underestimated, because usually only dissolved inorganic phosphorus (DIP) is measured while DOP be discharged. The concentration of DOP in the runoff and drainage flow did not increase along with increasing P application rates in this experiment. It indicates that the source of DOP is mainly the interior soil organic P dissolved by the runoff and drainage water.