Abstract: In order to clarify the effect of rice-crab symbiosis on the prevention and control of field diseases and weeds, three treatments： Rice monocropping continuous flooding mode （RM-F）, rice monocropping drying mode （RM-D） and rice-crab symbiosis mode （RC） were set up through micro-area experiments, and the occurrence of major weeds and rice blast in micro-areas and rice yield were investigated and analyzed. The results showed that the rice-crab symbiosis mode could basically control the harm of weeds, effectively control the occurrence of spirogyra, and significantly inhibit the occurrence of rice blast compared with the rice mono-cropping mode. The incidence of leaf blast decreased by 14.8 percentage points on average, the incidence of panicle neck blast decreased by 7.2 percentage points on average, and the rice yield decreased but the difference was not significant. Rice monocropping with drying model compared with continuous flooding model, the number of Schoenoplectus triqueter （L.） Palla and the incidence of rice blast were significantly increased, the incidence of leaf blast was significantly increased by 8.3 percentage points, the incidence of panicle neck blast was significantly increased by 4.5 percentage points, and the yield of rice had a tendency to decrease.

Key words: rice-crab symbiosis, water management, disease and weeds, yield, rice blast