Carbonate layer is one of the most important geothermal reservoirs in North China Region. The production and injection of carbonate geothermal wells in different secondary structural units is highly variable, seriously restricting regional development of the carbonate geothermal field. Acid- fracturing technology is efficient in increasing the yield and in maintenance of the carbonate reservoirs, which involves mass transport, acid- rock reaction, seepage and heat transfer, chemical heat release, and other complex processes. In this paper, a numerical method is proposed to simulate the acid- fracturing processes in the carbonate reservoirs taking the coupled thermal- hydraulic- mechanical- chemical interactions into consideration. The numerical method is verified by comparing with the previous experimental and numerical results. A model with heterogeneous fracture apertures in the carbonate reservoir is established to simulate the acid fracturing process and to evaluate the stimulation effect.