The oil and gas resources in carbonate reservoirs are occupy an important position in the field of exploration and development. Acid fracturing technology is regarded as a core method for the exploration and development of carbonate oil and gas reservoirs. The calculation model of conventional hydraulic fracturing is considered inapplicable to the calculation of acid fracturing processes. Therefore, the establishment of a net pressure calculation model inside artificial fractures and a fracture propagation model during the acid fracturing process is urgently needed. In this paper, the process of acid fracturing fluid entering and altering fractures is decomposed, and the pressure changes caused by each process are superimposed to obtain a two-dimensional model for calculating the net pressure within acid fracture. The reliability of the model is verified through calculations using fracturing operation curves. Then, combining Linear Elastic Fracture Mechanics (LEFM) theory with the net pressure calculation model, a pseudo-three-dimensional calculation model for acid fracturing cracks in carbonate reservoirs is established. The results show that the acid-rock reaction leads to a decrease in rock mechanical parameters, an increase in fracture space, a reduction in acid volume, and an increase in acid leak-off rate, all of which cause a reduction in net pressure within the fractures. The generation of CO2 from the acid-rock reaction causes an increase in net pressure within the fractures. As porosity and permeability increase, leak-off increases, net pressure decreases, and fracture size also decreases. As acid flow rate increases and acid viscosity increases, net pressure increases, and fracture size also increases. This study provides guidance for optimizing acid fracturing process parameters in carbonate reservoirs.