The infrared multiphoton decomposition of trichloroethylene-H(TCE-H) and trichloroehtylene-D(TCE-D) was studied by using the high power $CO_2$ laser. The pressure dependence of TCE-H decomposition showed that the HCl elimination channel to form ClC ≡ CCl was the major step at high pressures, while the HC ≡ CCl formation step became important at low pressures. $Cl_2C$ = CHCl ${ ightarrow}$ (high pressure) ClC ${equiv}$ CCl + HCl ${ ightarrow}$ (low pressure) HC ${equiv}$ CCl + 2Cl${cdot}$($Cl_2$) The IRMPD of TCE-H and TCE-D mixtures with 10P(20) laser line showed that optimum conditions of large isotope selectivity were the low system pressures and high laser powers. The experimentally observed dependence of the branching ratios on the pressure and laser fluence, and the isotope selectivity coefficients were quantitatively explained by using the modified energy grained master equations (EGME) model.