This paper presents a dynamic Computable General Equilibrium (CGE) model for China by incorporating the scale economy and imperfect competition into the MCHUGE model. Based on the Cournot equation, we derive a link between the share weighted price-cost mark-up across all firms in industry and the absolute degree of concentration (CRn) index and Hirschman-Herfindahl Index (HHI). Using the extension model, this paper gives an empirical illustration to analyse the impacts of the Chinese steel industry's Mergers and Acquisitions (M&As) on China's macro economy and industries.