A laboratory microcosm experiment was conducted under both the sterilized and unsterilized conditions to reveal the effects of water regime and temperature on the dissipation and transformation of chlorpyrifos in the overlying water-paddy soil system. It was found that, after application, chlorpyrifos in the overlying water and soil dissipated rapidly in the early stage and then the dissipation rate gradually decreased over time, which could be described by the first-order nonlinear equation. A high temperature of 40 ℃ favored the dissipation of chlorpyrifos in the overlying water and soil, while the presence of overlying water suppressed the dissipation of chlorpyrifos in soil. The unsaturated moisture condition led to a reduced dissipation rate constant of chlorpyrifos in soil, as compared to saturated conditions. The final residues of 3,5,6-trichloro-2-pyridinol (TCP; primary degradation product of chlorpyrifos) in the overlying water and soil were higher under the high temperature than under 25 ℃. The ratios of final TCP residue to applied chlorpyrifos in the soil without overlying water (19.70%-51.26%) were markedly higher than those in the soil with overlying water (0.71%-13.55%). At the high temperature, TCP residue was observed mainly in the overlying water, implying a high risk of TCP transport from the paddy field to surface waters via rainfall runoff in the summer.