Degradation kinetics and mechanism of tris(2-chloroethyl) phosphate (TCEP) by ultraviolet-persulfate (UV/PS) were explored, and toxicological assessment of degrading intermediate mixture was performed using isobaric tags for relative and absolute quantitation proteomic technology. This study was expected: (1) to investigate the degradation mechanism of TCEP by UV/PS, (2) to explore the potential application of proteomics for the safety evaluation of advanced oxidation processes, and (3) to prove the feasibility of applying moderate degradation for TCEP elimination.