Masonry structures have long been widely used due to their simplicity of construction and low cost. However, recent earthquakes have revealed significant structural damage in such buildings. Therefore, investigating their behavior to identify weaknesses and improve their seismic performance has become an important issue in urban construction. The purpose of this evaluation is to evaluate the seismic behavior of masonry walls with block masonry in thicknesses of 20 and 35 cm in the unretrofitted and retrofitted with CFRP sheets. The walls were modeled using the simplified micro modeling approach within the finite element framework in Abaqus software. The accuracy of the modeling technique was verified using three experimental specimens reported in the literature. Subsequently, the seismic performance of the walls was assessed by analyzing their hysteretic behavior and the corresponding idealized response curves. The results indicate that, in the unstrengthened condition, the 35 cm wall exhibited 45% higher ductility and 12% greater effective stiffness, while its strength degradation was 31% lower compared with the 20 cm wall. In the strengthened condition, the 35 cm wall demonstrated improvements of 73%, 6%, 36%, and 41% in ductility, load bearing capacity, effective stiffness, and dissipated energy, respectively, while its strength degradation was 7% lower than that of the 20 cm wall.