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In order to provide the scientific basis for the environmental risk assessment of cycloxaprid and 6-Cl-PMNI (intermediate of cycloxaprid), the degradation properties of 6-Cl-PMNI in aerobic, anaerobic and/or sterile soil, as well as in water with different pH values at different temperature were explored under laboratory conditions using HPLC for its kinetics study and UPLC-MS/MS for the identification of its metabolites/degradation products. Fortification study showed that the recoveries of 71.4–100.5% with the maximum coefficient variation (CV) of 7.47% were obtained. The linear range was 0.1–10 mg/L with the good linearity of R 2 = 0.9990. For standard, the method LOD (limit of detection) and LOQ (limit of quantification) was 0.03 mg/L and 0.1 mg/L, respectively. Results demonstrated the good performance of the developed method. Kinetics study indicated that the degradation half-lives (t 0.5 ) in pH 3-pH 10 buffers varied from 111.8 d to 288.8 d at 25 °C but rapidly shortened to 1.6–25.7 d at 70 °C. Good negative linear ships (R 2 ≥ 0.8423) between half life and temperature were found. 6-Cl-PMNI could be readily degraded in non-sterile soil (t 0.5 0.8–7.5 d) while slowly degraded in sterile soil (t 0.5 64.8–91.2 d). Three hydrolytic products and one metabolite of 6-Cl-PMNI in aerobic soil were identified. The C C olefinic bond reacted with H 2 O by Markovnikov Additive Reaction and the split of C–Cl were mainly proposed as the possible reaction pathway for 6-Cl-PMNI degradation in water and in soil, respectively. [ABSTRACT FROM AUTHOR]