<p>To address the issue of non-uniform fracture propagation among clusters in multi-stage fracturing of horizontal wells, a numerical model for multi-cluster temporary plugging and diversion fracturing (TPDF) in horizontal wells is developed in this study. Building upon the multi-fracture propagation model, the effective perforation number and the perforation friction after temporary plugging ball (TPB) seating are incorporated, enabling continuous simulation of the multi-cluster flow redistribution and fracture propagation throughout the entire pre- and post-plugging process. A systematic sensitivity analysis is performed to evaluate the effects of the injection rate, the number of TPBs, and the TPB pumping timing on the propagation uniformity of multi-cluster fractures, and the temporary plugging design is optimized using the coefficient of variation of the fracture half-length as the quantitative evaluation indicator. The results indicate that: 1) at a low injection rate (8 m³/min), the fluid provides insufficient carrying capacity and the seating success rate is low, whereas at a high injection rate (14 m³/min), the TPBs are prone to dislodgement, resulting in degraded seating stability; an injection rate of 10–12 m³/min is therefore recommended; 2) an inadequate number of TPBs fails to sufficiently suppress the dominant fractures, while an excessive number leads to inadvertent sealing of non-target perforation clusters; the recommended number of TPBs is 1.0–1.25 times the perforation number per cluster; 3) premature pumping of TPBs results in inadequate overall fracture development, whereas delayed pumping causes over-extension of the lateral fractures and restricted propagation of the middle cluster; a pumping timing within 0.2–0.5 of the total operational time is therefore recommended. The proposed model and optimization results provide a theoretical foundation and reference for the design of multi-cluster TPDF operations in horizontal wells.</p>