The thermal reaction of trichloroethylene (TCE: C2HCl3) has been conducted in an isothermal tubular flow reactor at 1 atm total pressure in order to investigate characteristics of chlorinated hydrocarbons decomposition and pyrolytic reaction pathways for formation of product under excess hydrogen reaction environment. The reactions were studied over the temperature range 650 to 900 ℃ with reaction times of 0.3-2.0 s. A constant feed molar ratio C2HCl3 : H2 of 4 : 96 was maintained through the whole experiments. Complete decay (99%) of the parent reagent, C2HCl3 was observed at temperature near 800 ℃ with 1 s reaction time. The maximum concentration (28%) of C2H2Cl2 as the primary intermediate product was found at temperature 700 ℃ where up to 68% decay of C2HCl3 occurred. The C2H3Cl as highest concentration (19%) of secondary products was detected at 750 ℃. The one less chlorinated methane than parent increased with temperature rise subsequently. The number of qualitative and qualitative chlorinated products decreased with increasing temperature. HCl and dechlorinated hydrocarbons such as C2H4, C2H6, CH4 and C2H2 were the final products at above 800 ℃. The almost 95% carbon material balance was given over a wide range of temperatures, and trace amounts of C6H6, C4H6 and C2HCl were observed above 800 ℃. The decay of reactant, C2HCl3 and the hydrodechlorination of intermediate products, resulted from H atom cyclic chain reaction via abstraction and addition replacement reactions. The important pyrolytic reaction pathways to describe the important features of reagent decay, intermediate product distributions and carbon mass balances, based upon thermochemical and kinetic principles, were suggested. The main reaction pathways for formation of major products along with preliminary activation energies and rate constants were given.