Methanol is a promising fuel to suppress knock for improving engine compression ratio. In this study, knock combustion was simulated in a downsized spark engine with different methanol-isooctane blends. The pressure and temperature evolution profiles of these mixtures during knocking were obtained and showed that knock here originated from the intensive interaction between pressure wave and the heat released from auto ignition, which leaded to some other hot-spots. While using 5% methanol, the intensity of chemical reactions was reduced sharply comparing with that of pure isooctane, which lowered the heat release rate and successfully reduced the intensity of knock. The reactions below temperature of 950 K gradually become slower with methanol content increasing to 10% and 15%. However, the accelerated reactions made fuel consumed faster once it exceeded this certain temperature limit, which leaded a slight increase in knock intensity. The outcome of this work is potentially useful for comprehending the knock process of methanol.