The improved and expanded two-scale continuum model is employed in this chapter to study and elucidate the acidizing processes and mechanisms in complex carbonate rock matrices. Different stopping conditions are used to simulate and discuss various treatment objectives in the matrix acidizing process. The model incorporates matrix acidizing theories to assess the impact of different treatment degrees on the acidizing outcomes. Additionally, numerical examples are designed to illustrate the targeting mechanisms and optimization principles in the design of functional acidizing fluids for carbonate rock matrices. For the optimum design of a matrix acidizing acid fluid system aimed at reducing construction difficulty (by lowering injection rate) and minimizing construction costs (by reducing injection time and breakthrough volume), the diffusion co-efficient of the acid fluid can be used as a target parameter. Lastly, numerical examples are designed to examine the impact of isolated fracture and vug parameters on the results of acid stimulation. Although these fractures and vugs may be well-developed, their properties have a limited contribution to the hydraulic parameter. The presence of isolated fractures and vugs can significantly reduce the consumption of acid fluid required for breakthrough into the target formation without a noticeable effect on the optimum injection rate for wormhole formation.