Tri(2-chloroethyl) phosphate (TCEP) with the initial concentration of 5 mg/L was degraded by UV/H2O2 oxidation process.The removal rate of TCEP in the UV/H2O2 system was 89.1％ with the production of Cl-and PO43-of 0.23 and 0.64 mg/L.The removal rate of total organic carbon of the reaction was 48.8％ and the pH reached 3.3 after the reaction.The oxidative degradation process of TCEP in the UV/H2O2 system obeyed the first order kinetic reaction with the apparent rate constant of 0.0025 min-1 (R2=0.9788).The intermediate products were isolated and identified by gas chromatography-mass spectrometer.The addition reaction of HO· and H2O and the oxidation reaction with H2O2 were found during the degradation pathway of 5 mg/L TCEP in the UV/H2O2 system.For the first time,environment risk was estimated via the “ecological structure activity relationships” program and acute and chronic toxicity changes of intermediate products were pointed out.The luminescence inhibition rate of photobacterium was used to evaluate the acute toxicity of intermediate products.The results showed that the toxicity of the intermediate products increased with the increase of reaction time,which may be due to the production of chlorine compounds.Some measures should be introduced to the UV/H2O2 system to remove the highly toxic Cl-containing compounds,such as a nanofiltration or reverse osmosis unit.