Abstract: Outdoor-cage studies were conducted in Beijing in 1988 on the control effects of common ragweed with Zygogramma suturalis, a potential biological control agent introduced from USSR. Introduction of 2 1st instar larvae on the ragweed seedlings at its 4-leaves stage resulted in an optimal control. By maturation of the larvae, 95.7%of the host leaves were destroyed. The adult control effects improved as the density of the adults introduced into the plots increased. When 65 adults were introduced into a plot of 12 host plants with 10 leaves each, 81.2% of the leaves were destroyed after 24 days. In the following year, the number of host plant germinated in the adult-controlled plot was 4.3 times of that in the previous autumn, compared with the reproduction rate of 33.8 times in the control plot with no beetles. The consumption rate by the adults was found to be a constant of 0.067% per adult per day. No population interference was observed when the adults aggregated on the hosts. An integrated fuzzy judgment model was proposed the evaluation of the control effects by Zygogramma suturalis. The model was thought to be comprehensive, flexible, and practical.