In thermodynamic analysis of internal combustion engine, the specific heats of working fluid is considered to be constant. Due to specific heats are functions of operation temperature of cycle, this consideration cause to several errors in the thermal analysis. In this paper, standard Otto cycle with three various types of specific heats ratios has been analyzed numerically and effect of these ratios on the thermal performance of cycle such as specific output work and thermal efficiency has been studied and results has been investigated. For three types of specific heats ratio, these ratios are considered constant, linear function of operation temperature of cycle and polynomial function of cycle temperature. Results showed that both linear and polynomial specific heats ratios gave approximately same results such as specific output work and thermal efficiency and there are difference between thermal result of both linear and polynomial type with constant ratio. Also CPU time consumption and required memory usage for analyzing these here type had been evaluated . all results mentioned that linear specific heats ratio should be considered for the design of practical Otto cycle.