Abstract: 【 Objective 】 Based on the synergistic use of synergists and herbicides, we focused on chemical control of ragweed Ambrosia artemisiifolia L. and giant ragweed Ambrosia trifida L. by reducing pesticide and increasing efficiency technique.【 Method 】 Field plot experiment was conducted to compare and analyze the field control effect of two under 15%, 30% and 50% reduction.【 Results 】 Jijian had better control effect on plant and fresh weight on the 45 days or 78 days after herbicide at 15%, 30% and 50% drug reduction levels with synergist, and the control effects were 64.23%-98.84% and 65.37%-98.09% respectively for ragweed or giant ragweed. At the level of 15%, 30% drug reduction, the control effects of the two herbicides were 99.24%, 97.59% and 100.00%, 97.69% respectively after 45 days or 78 days, the control effect of the treatment combined with synergist Jijian was 87.70%-98.65% and 88.77%-97.96%, respectively. And the control effect was similar to that of the plant with the optimum dosage in the field, and the difference was 0.59%-11.54% and 0.27%-11.23%, respectively. Under 50% drug reduction with synergist Jijian, the control effects were 54.30%-67.00% and 55.63%-67.14% respectively, and the control effect was lower than the sui Table dosage in the field, whose difference was 30.59%-44.94% and 30.55%-44.37% respectively.【 Conclusion 】 21% aminopyralid AS 17.50 mL /667m², 75% saflufenacil and glyphosate WG 42.00 mL /667m², the occurrence and damage of ragweed with plant height of 23 cm or so in May and 12 cm or so in June can be effectively controlled by adding synergists, so it is feasible to reduce the application rate by 30%, but the synergistic effect of different synergistic agents is different to some extent. In actual production, it is recommended to use the synergist Jijian 15.00 mL /667m², followed by synergist Orange Peel oil 15.00 mL /667m².