Abstract: To develop low-foam pesticide adjuvants, an novel allyl polyoxyethylene methyl ether modified trisiloxane surfactant ( 2a) was prepared by adding heptamethyltrisiloxane to allyl polyoxyethylene (n = 7) methyl ether ( 1a) . The structure of 2a was confirmed by FT-IR and ¹H NMR. The surface tension of the 2a aqueous solution with a mass fraction of 0.1% was lower than 20.50 mN/m. The 30 s spreading diameter was 52.5 mm. And the foam volume was 36 mL. Overall, its comprehensive performance is comparable to foreign low-foam pesticide additives. Compared with the widely used pesticide adjuvant FGM683, 2a could reduce the amount of foam by more than 50%. The results of indoor biological activity tests showed that after adding 0.1% of 2a to thiamethoxam 250 water-dispersible granules (WG), the LC₅₀ value to N. lugens was 1.55 (1.27-1.82) mg/L, while the LC₅₀ value without 2a was 2.01 (1.71-2.34) mg/L. Field test results showed that when 2a at the dose of 90 g/hm² was added to the thiamethoxam 250 WG at the dosage of 225 g/hm² , the control effect on N. lugens was increased by 5.8% 3 days after drug application and increased by 9.0% 7 days after drug application. The results of this study show that low foam polyether modified trisiloxane 2a can significantly increase the control effect of thiamethoxam 250 WG on N. lugens. It can be used as a tank mixing aid for the control of N. lugens in rice fields.