In recent days, further improvement of efficiency in SI engine has been required. To achieve it, the reduction of heat loss is an important issue because it accounts for 20-30% of the amount of total heat release from the fuel. However, wall heat transfer which is the dominant physical phenomena in the heat loss is a very complex phenomenon because it affect with flame propagation and knock, so it has yet to be clearly proved especially in the conditions of high boosted, high EGR ratio and lean mixture. The objective of this research is to elucidate the mechanism of the cooling loss by measuring the combustion chamber wall temperature and in-cylinder gas temperature under the supercharged, high EGR and lean mixture condition.