This study is to estimate the cost of constructing Korea chemical process plant at predesign stage. This study deduced a theoretical equation which can afford to modify quantitatively the changeable relation of the construction cost, resulting from the substitution of all foreign equipments for the domestic ones, by means of setting the new concepts-domestic factor（R_E, R_M, R_L）, the difference-value factor(α_E, α_M, α_L) and considering the mutual relation between these two factors. The theoretical equation provided the estimation model for the cost of constructing Korea chemical process plant, based upon [factor system]. Analyzing the precendents in investigating the real cost spent for constructing the domestic chemical plants, which was carried out to find out the validity of this model, showed a good result error range of 3.33 % comparing with the overall factor in real construction cost.