Abstract: he functional response of C. sinica. an important polyphagous predator of cotton pests in China, to cotton aphid (Aphis qoaaypii) and cotton bollworm (Heliothis armigera) were determined as Hoiling's type II in the experiments conducted from in BeiJing. The searching efficiency (E') of the predator varied with temperature. Results of simulation showed the minimum threshold temperature (Ti) for the searching efficiency as 8.3°C, the maximum threshold temperature (Tm) as 41°C, abd the potential attacking rate (K) being O.42. Results of the laboratory test showed that the predator prefers cotton aphid to cotton bollworm.