Considering the limitations of finite difference software in simulating the distribution of pore water pressure in unsaturated soil slopes under rainfall infiltration conditions, secondary development of the software was conducted using the FISH programming language. A relationship between the permeability coefficient of unsaturated soil and matric suction was established, enabling the simulation of anchor-reinforced slopes under rainfall infiltration conditions. The study analyzed the reinforcement effects of anchors under three anchor inclination angles (10°, 20°, and 30°) and three anchor lengths (6 m, 8 m, and 10 m). The analysis focused on slope displacement, pore water pressure, saturation, shear strain, safety factor, and axial force and shear force of the anchors. The results show that, in terms of the influence of anchor reinforcement on slope stability, an anchor inclination angle of 30° is optimal. At this angle, the shear force distribution among the three anchors is uniform, and the anchors provide significant shear resistance along the weak sliding surface. The anchoring effect improves significantly as anchor length increases from 6 m to 8 m; however, the improvement from 8 m to 10 m is not pronounced. Considering safety and economic factors comprehensively, an anchor length of 8 m is determined to be optimal. Under a 12-hour rainfall duration and a rainfall intensity of 90 mm/h, the unreinforced slope experienced overall sliding failure, whereas the reinforced slope showed significantly reduced displacement. No sliding occurred at the slope toe, and the slope crest exhibited a small arc-shaped displacement zone. The second row of anchors was identified as the displacement boundary, indicating that the anchors effectively resisted shear forces and reduced slope displacement to maintain stability. For unreinforced slopes, the shear strain increment contours after 12 hours of rainfall revealed overall sliding failure, while the reinforced slope exhibited uniform distribution with no continuous sliding zones. Moreover, anchors arranged with optimal parameters maintained the safety factor of the reinforced slope above 1.25 under 12 hours of continuous heavy rainfall, satisfying engineering requirements for slope stability under extreme rainfall conditions.