A barrels planted experiment was conducted to study the effects of PASP-Ca with different concentration levels on the dynamic changes of NH₄⁺, NO₃^- and total nitrogen (TN) concentrations in surface water of paddy field. The result showed that the concentrations of TN, NH₄⁺ and NO₃^- in the surface water of paddy field reached the maximum within 1 day, 3 days and 9 days respectively after nitrogen application. NO₃^-/TN was less than 0.1 and (NH₄⁺+NO₃^-)/TN was more than 0.5. Therefore, NH₄⁺ and TN could be used as the main monitoring indicators, and NO₃^- as an auxiliary indicator for the prevention and control of farmland water pollution. Adding a certain concentration of PASP-Ca had slow release effects for the changes of nitrogen concentrations in surface water of paddy field, while the effects of PASP-Ca at 0.3% concentration level was relatively better, the reduction rates of NH₄⁺ and TN in surface water of paddy field were 3.452 mg/(L·d) and 4.806 mg/(L·d) respectively. Compared with apply nitrogen only (CK), the reduction rates by 11.68% and 16.25%. Meanwhile, the average concentration of NH₄⁺ was 6.999 mg/L, which was 3.88% lower compared with CK. The average concentration of NO₃^- was 0.396 mg/L, which was 24.83% lower compared with CK. The average concentration of TN was 20.077 mg/L, which was 3.10% higher compared with CK. The dynamic changing trends of NH₄⁺ and TN concentrations with time could be expressed by logarithmic equations. After nitrogen application, the TN concentrations in paddy field decreased logarithmically with time, while the concentrations of NH₄⁺ increased logarithmically in 3 days, and then decreased logarithmically with time. 9 days after nitrogen application was the key stage to prevent nitrogen loss in surface water of paddy field.