Abstract: In order to clarify the synergistic action of the mixtures of boscalid and pyrametostrobin against Botrytis cinerea, the inhibitory activity of the mixtures at different mixing ratios to isolate DZ3 was determined by mycelial growth rate method, and the synergistic radio was calculated according to the Wadley formula. The inhibitory activity of the best mixture to the other five isolates of B. cinerea was determined by inoculating fungicide-sprayed cucumber cotyledons with conidial suspension, and the control efficacy against tomato grey mould was determined in the field. The synergistic mechanism of the best synergistic combination was studied by detecting the content of dissolved oxygen, conductivity of the conidial suspension of isolate DZ3, and the content of malondialdehyde in the hyphae of isolate DZ3. The results showed that the mixtures of boscalid and pyrametostrobin (9 :1, 7 :1, 5 :1, 3 :1, 1 :1, 1 :3, 1 :5, 1 :7 and 1 :9,m/m) exhibited synergistic activity against the mycelial growth of isolate DZ3, and the 1 :3 mixture exhibited the most significant synergistic effects, with synergistic ratio up to 4.76. The 1 :3 mixture also showed synergistic inhibition to the other five isolates of B.cinerea. The control efficacy of the mixture (1 :3, m/m) against tomato gray mould in the field was 78.05%-93.96% at 200-300 g a.i./hm2, and the inhibitory activity of the mixture (1 :3, m/m) on the respiration of isolate DZ3 was similar to that of boscalid, but the impact on membrane permeability and mycelium membrane lipid peroxidation was more significant than that of individual boscalid and pyrametostrobin. The results of present study suggested that the mixture of boscalid and pyrametostrobin (1 :3, m/m) could be used in controling of tomato gray mould.