Abstract: This paper reports the degredation tendency of prothiofos on pine needles as compared with Fenthion. Both Prothiofos and Fenthion belong to the kind of organic phosphoros insecticides with relative lower rate of tendency. The prothiofos diluted with 0. 5% polyvinyl alcohol is able to improve its stickness, prolong the effective periods of insecticides and reduce environmental pollution.