This dissertation was mainly concerning with studies on photochemical degradation of alachlor irradiated by high pressure mercury lamp(HPML). The following effects on phtolysis of alachlor were investigated: the water types, pH buffers, fertilizers, dyes, metallic ions, hydrogen peroxide and surfactants. Photolytic rates of alachlor in organic solvents under HPML were investigated as well. And photolytic rates of alachlor were studied while alachlor and another chemical was absorbed on quardz sa...