The direct hydrogen abstraction reactions of Cl atom with SiHnCl4-n (n=1,2,3,4) have been studied systematically using ab initio molecular orbital theory. Geometries have been optimized at the MP2 level with 6-311+G(d) basis set, QCISD(T)/6-311+G(d,p) has been used in the final single point energy calculation. The kinetic calculations of these reactions have been explored using the canonical variational transition (CVT) state theory method with small-curvature tunneling (SCT) effect correction over the temperature range of 200-2000 K. The CVT/SCT rate constants exhibit typical non-Arrhenius behavior and three-parameter rate-temperature formulas have been fitted for the reactions of Cl with SiH4, SiH3Cl, SiH2Cl2, and SiHCl3, respectively (in unit of cm3 molecule-1 s-1). The calculated CVT/SCT rate constants are in agreement with the available experimental values. (C) 2004 American Institute of Physics.