Through field experiments，the effects of the long-term integrated rice-crayfish mode and the rice monoculture mode on potassium(K)input and output characteristics，balance status，and different K application rates on the yield of direct-seeded rice and potash fertilizer use efficiency were studied.The results showed that the K input of the integrated rice-crayfish mode was 134.3 kg/hm²，which were mainly brought by chemical fertilizer，fodder，rainfall and irrigation water，accounting for 46.3%，10.3%，5.5% and 34.8% of the total input，respectively.Compared with the rice monoculture mode，the K input of fodder and irrigation water of the integrated rice-crayfish mode increased greatly.The total K output of the integrated rice-crayfish mode was 119.4 kg/hm²，mainly including rice grain，commercial shrimp，leakage and runoff，accounting for 26.5%，5.0%，41.2% and 27.3% of the total output，respectively.Compared with the rice monoculture mode，the K output of the above four ways increased significantly.The apparent balance of K in the two modes was surplus，and the surplus of K in the integrated rice-crayfish mode was lower than that in the rice monoculture mode.Under the same K application rate，the rice yield，K partial productivity and K utilization rate of the integrated rice-crayfish mode were 14.1%，14.2% and 5.6% higher than that of the rice monoculture mode respectively.Compared with the rice monoculture mode，the long-term integrated rice-crayfish mode could increase the yield mainly by increasing the number of effective panicles.In a word，when the K application rate of the integrated the rice monoculture mode and rice-crayfish mode of rice and shrimp reach 47.3 kg/hm(K2O application 57.0 kg/hm²)and 21.6 kg/hm²(K2O application 26.0 kg/hm²)，respectively，the K balance of farmland ecosystem could be maintained；when the K2O application amount reach 82.2 and 85.0 kg/hm² respectively，higher yield could be gotten.