The reaction mechanisms between some products formed from the reaction of $Si^+\,+CH_4$ have been studied by ab initio quantum mechanical approaches. The GAUSSIAN 88 package was used for the geometry optimization and for finding transition states. the mechanism involves the initial interaction of $Si^+$ with $CH_4$ to give three different kinds of complexes. The doubly and triply bridged complexes experience the same transition state on the way to $CH_3SiH^+$, which then isomerizes to $CH_2=SiH_2\,^+$. The singly bridged complex, if formed, directly dissociates to give $CH_3+SiH^+$ and $CH_3\,^+\,+\,SiH$. Compared to the starting species, the doubly and triply bridged complexes are stabilized by 5.0 and 4.8 kcal/mol, respectively, and the singly bridged complex is largely destabilized by 30.3 kcal/mol. the singly bridged complex is actually considered to be a transition state leading to the dissociated products. From $CH_2=SiH_2\,^+$, some other products are obtainable. The structures of all the species have been determined by the complete geometry optimization at the HartreeFock level of theory with several basis sets including 6-31G$^\ast$ basis set and at the MP2/6-31G$^\ast$ level of theory. The transition states have been characterized by the presence of one and only one negative eigenvalue of the force constant matrix(one imaginary vibrational frequency), Hessian matrix.