Abstract: In order to discover effective herbicide tank mixing adjuvants, increase the efficacy of metamifop and reduce the dosage of active ingredients, seven kinds of methylated vegetable oils were synthesized by the principle of base-catalyzed transesterification. Maize oil, peanut oil, rapeseed oil, soybean oil, sunflower oil, castor oil and sesame oil were used as the raw materials. Twenty kinds of tank mixing adjuvants were mixed in different proportions after the addition of emulsifier. The synergistic effect of 20 adjuvants with metamifop were studied by indoor experiments. The results showed that when the volume fraction of methylated vegetable oil adjuvant was 0.5% of the spray volume, the retention of metamifop on Echinochloa oryzicola Vasing leaves was significantly increased, and the range of increase was11.17%-143.60%. Besides, the surface tension and contact angle of metamifop solution were also decreased by 9.67%-27.34% and 8.72%- 65.60%, respectively. Twenty kinds of methylated vegetable oil adjuvants had synergistic effects on the control of E. oryzicola with metamifop, among which methylated vegetable oil adjuvant JZ-4 m (methylated peanut oil): m (methylated maize oil) = 2 : 1, emulsifier m (OP-7) : m (PEG-400) : m (ZR-5) = 1 : 1 : 0.5, the content was 20% of the quality of methylated vegetable oilwas the best one. Compared with the plant treated by metamifop(120 g/hm²) without adjuvant, plant death rate was increased by 45.00% and fresh weight inhibition rate was increased by 25.53% after the addition of methylated vegetable oil adjuvant JZ-4. Comprehensive analysis demonstrated that the best adjuvant for the control of metamifop against E. oryzicola was methylated vegetable oil adjuvant JZ-4.