The improved two-scale continuum model is used in this chapter to simulate and reveal the mechanisms of carbonate rock acid stimulation. The improved two-scale continuum model successfully reproduces the observed matrix dissolution curves and typical dissolution patterns in carbonate acid stimulation experiments and captures the optimum injection rate of the acid fluid. The classical two-scale continuum model is solved as a reference solution to quantitatively study the influence of model improvements on the results of acid stimulation. The applicability of the Darcy equation is limited to describing the momentum transport process of acidizing fluids at high injection rates. Based on the improved two-scale continuous model, numerous numerical examples are designed to discuss the effects of fluid property and solid matrix property parameters on the acid stimulation process. The properties of the acid fluid not only affect the equilibrium conditions for wormhole formation during acid stimulation but also impact the efficiency of acid usage. The properties of the solid matrix have an impact on the efficiency of acid fluid utilization.