The invention relates to the technical field of modern agricultural cultivation, and discloses a water quality regulator for fish cultivation in rice fields. The prepared water quality regulator can guarantee the maximum supply of nutrients in the rice growth period by intervening the element content of rice field culture water in the rice growth process, and improve the fish culture environment,and a rice field-fish composite ecological system is constructed, so that the yield and quality of aquatic products are improved, and the rice field water eutrophication problem is solved. By means ofthe culture mode, the whole rice field system has high self-purification capacity, benign growth and reproduction of organisms in water are kept, the water environment is stable, the water changing frequency is remarkably reduced, the cost is reduced, culture losses caused by water quality pollution are avoided at the same time, mutual utilization of rice and aquatic metabolites is achieved, andthe dynamic balance of a rice culture system is realized; and the adverse effects of eutrophication on aquaculture are reduced, the cost investment can also be reduced, the fish culture benefit is improved, and the problems of low quality, poor benefit and large pollution of the aquatic products cultured in the existing rice field are solved.