【Objective】Because of extensive management of water and nutrients in rice cultivation, especially artificial drainage of just fertilized paddy fields for mechanized rice transplanting and direct rice seeding, non-point source N and P pollution turned out to be very serious in Jianghan Plain, posing a great threat to the safety of agricultural water and drinking water. N and P in paddy field surface water are the direct sources of non-point source N and P pollution. It is, therefore, essential to master rules of the changes in N and P in paddy field surface water to preventing and controlling the non-point source N and P pollution from paddy fields. However, at present, it is still unclear how N and P changes in paddy fields surface water and how fertilizer application affects the changes in the Jianghan Plain. This is a topic that calls for further studies. 【Method】In this study, a field experiment, designed to have a number of treatments varying in N and P application rate along a gradient, was carried out to explore how N and P changes in paddy field surface water and how fertilizer application affects the changes. Samples of paddy field surface water were collected for 8 consecutive days after each fertilizer application for analysis of total N (TN), total soluble N (DTN), soluble organic N (DON), NH₄⁺-N and NO₃^--N, total P (TP), total soluble P (DTP), and particulate P (PP). 【Result】Results show that total soluble N (DTN), soluble organic N (DON) and NH₄⁺-N accounted for 88.0%, 44.7% and 31.6%, respectively, of the total N (TN) in surface water, after application of urea, and increased with increasing N application rate, while particulate P (PP) made up 76%~93% of the total P (TP) after application of superphosphate, but decreased with increasing P application rate. A piecewise linear correlation was observed between N concentration in surface water and N application rate. With increasing N application rate, N in surface water would increase in concentrations, and when N application rate exceeded 287.8, 289.9, 231.5 and 336.7 kg·hm^-2, TN, DTN, NH₄⁺-N and DON would jump by a large margin, respectively. All forms of P in surface water would increase linearly in concentraton with increasing P application rate. TN and DTN peaked 1 day after urea application, and then leveled off 5 days after basal and tillering fertilization and 2 days after panicle fertilization. NH₄⁺-N reached its peak value 2 days after basal and tillering fertilization and 1 day after panicle fertilization, and then leveled off 5 days after basal and tillering fertilization and 2 days after panicle fertilization. TP, PP and total soluble P (DTP) reached their respective peak values quickly just in 1 day, and then decreased sharply by over 79.0% 3 days after superphosphate application. 【Conclusion】DTN, especially DON and NH₄⁺-N are the main forms of N in surface water after urea applicaton. PP is the main form of P after superphosphate application. Reducing the N and P application rates can reduce the concentrations of N and P in surface water and their losses as well. So it is advisable to control N application rate within 231.5 kg·hm^-2. The first 5 days after basal and tillering fertilization and 2 days after panicle fertilization were the optimal periods key to controlling N loss from paddy fields, and 3 days to controlling P loss.