Abstract: 【Objective】 The purpose of the study was to investigate the effect of coumoxystrobin,prochloraz and their combination on Rhizoctonia solani Kühn,and the field control efficacy of this disease,so as to provide theoretical basis for the field control of rice sheath blight.【Method】 Used R. solani as material in the indoor in vitro condition,the bioactivity of coumoxystrobin TC and prochloraz TC and their combination against R. solani was determined by mycelium growth rate method. The optimal ratio was screened out to preliminarily analyze the synergistic mechanism of the combination against rice sheath blight. According to the optimal ratio,the field efficacy tests were carried out.【Result】The results showed that coumoxystrobin TC and prochloraz TC single dosage had good inhibitory effects on the mycelial growth of R. solani,and the effective inhibitory concentrations(EC₅₀)were 1.47 and 0.61 μg/mL respectively. The combination of coumoxystrobin TC and prochloraz TC at the mass ratios of 1:4,1:2,1:1,2:1 and 4:1 had inhibitory effects on the mycelial growth of R.solani,and the EC₅₀ was in the range of 0.12-0.24 μg/mL. Among them,the synergistic effect was most significant when the combination of coumoxystrobin and prochloraz at the mass ratio of 4:1,with an EC₅₀ of 0.12 μg/mL, and a cotoxicity coefficient(CTC)of 955.81. Field test results showed that the combination of 20% coumoxystrobin SC and 25% prochloraz EC with the active ingredient mass ratio of 4:1 (48 g/ha+12 g/ha)had a high control effect of 84.85% on rice sheath blight at 21 d post-dose,which was extremely sgnificantly higher than the control effects of 20% coumoxystrobin SC(73.58%)and 25% prochloraz EC(72.79%)as single agent(P<0.01). The combination of coumoxystrobin and prochloraz with the active ingredient mass ratio of 4:1 could improve the permeability of cell membrane of R. solani damage the integrity of the cell membrane,and increase the content of soluble protein.【Conclusion】 The synergistic effect of the combination of coumoxystrobin and prochloraz with the active ingredient mass ratio of 4:1 is significant,and it has a better synergistic control effect on rice sheath blight,and greatly reduces the amount of pesticides used. It has the potential to be developed into a combination of synergistic preparations for rice sheath blight.