To provide a theoretical basis to use appropriate nitrogen （N） amount for accurate fertilization in the rice-crayfish co-culture system, the effects of different nitrogen amounts on rice yield and surface water quality were studied. Five N application rates were set at N 0, 60, 120, 180 and 240 kg/hm² based the same ratio of basal fertilizer to tillering fertilizer （7∶3）, which was represented by CK, N₆₀, N₁₂₀, N₁₈₀ and N₂₄₀, respectively. The results showed that fertilization could maintain a higher inorganic N content in the soil and promote dry matter accumulation in rice. The fertilization treatments increased rice yield by 8%~42%, of which N₁₂₀ obtained the highest yields, which is 42% higher than CK. After nitrogen application, the ammonia N content in the surface water increased rapidly at the first 3 days and then decreased. After 14 days, it dropped to the lowest and became stable. Among them, the ammonia N concentration of different treatments within 5 days after nitrogen application was significantly different, and the value increased as the nitrogen fertilizer amount increased. The nitrite N concentration in surface water increased at first 6 days, then decreased and then increased. The difference between the fertilization treatments on the 3rd day was significant, and the difference between the treatments after the 7th day was not significant. Different nitrogen application amounts affected the pH of the surface water. The pH fluctuation of each treatment within 14 days after fertilization was between 6.57 and 8.22, but the difference between the treatments was not significant after 14 days. The appropriate amount of nitrogen application promotes the increase of rice yield, but also reduces the content of ammonia N and nitrite N in the field surface water, maintaining a good living environment for crayfish, and 120~130 kg/hm² can be used as the recommended nitrogen application rate for rice-shrimp co-cropping system.