Wettingdrying alternation irrigation, which has a higher grain yield than traditional flooded rice because the water regime is more favorable to yield formation, is considered as an important watersaving cultivation technology in rice plants. In addition, the two different irrigation regimes have significant effects on ratios of ammonia nitrogen and nitrate nitrogen in the root zone, and then could alter the growth and development of rice plants. Therefore, soil water and nitrogen forms could be critical regulatory factors affecting yield formation of rice plants in wettingdrying alternation irrigation. To investigate the interaction effect, we conducted pot experiments in 2016 with cultivar Ningjeng 8 in different water regimes and N forms. In this study, water regimes included traditional flooding irrigation (W₁) and wettingdrying alternation irrigation (W₂), and N forms treatments set three categories：ammonia and nitrate nitrogen ratio=0∶100 (N₁), ammonia and nitrate nitrogen ratio=50∶50 (N₂), ammonia and nitrate nitrogen ratio=100∶0 (N₃). The results showed that: (1) the grain yield, yield components, photosynthetic production, harvest index, N harvest index, and nitrogen grain production efficiency in the W₂ treatment are significantly higher than that in the W₁ treatment (_P<0.05). But slightly lower N content in the W₂ treatment was observed when compared with the W₁ treatment. From the perspective of N forms, grain yield in the N₂ treatment was the greatest, and yield in the N₁ treatment was the minimum among N treatments, which were mainly from a higher matter translocation from sheath to kernel and photosynthetic produce ability during grain filling stage in the N₂ treatment than that in the N₃ and N₁ treatments. The greater N content and N concentration could be an important physiological basis for high photosynthetic ability in the N₂ treatment than the others. The N₁ treatment had the highest N use efficiency, and then followed by the N₂ and N₃ treatments. Moreover, there were significant interaction effects between water regimes and N forms for grain yield, yield components, and harvest index (P<0.05). The W₂ treatment coupled N₂ treatment was the optimal combination for yield formation of rice plants.