The cationic polymerization of substituted oxetanes which have pendant energetic groups such as methoxy, azido, and nitrato are investigated using the semiempirical CNDO/2, MINDO/3, MNDO, and AM1 methods. The nuclephilicity and basicity of substituted oxatanes can be explained by the negative charge on oxygen atom of oxatanes. The reaction of the energetic cyclic oxonium ion forms to the open chain carbenium ion forms is expected by computational stability energy of the oxonium and carbenium ion(about 10 ~ 20 Kcal/mole) favoring the carbenium ion. The prepolymer propagation step SN1 mechanism will be at least as fast as that for SN2 mechanism.