Abstract: To investigate the mechanism of active earth pressure unloading and the direction change of sliding thrust under the influence of unloading conversion plates in retaining walls, this experiment employs a self-designed model box. The setup includes no internal plates or one to multiple rigid plates arranged at specific inclination angles. Using steel stress gauges and the tie-back method, the resultant earth pressure on the retaining wall is measured. Theoretical calculations are conducted for the earth pressure resultant after installing horizontal plates and load transfer plates, followed by comparative analysis with measured values. Particle image velocimetry (PIV) technology is used to analyze the plastic zone evolution in the soil during the experiment. The results indicate that: (1) the installation of a load transfer plate structure effectively alters the direction of sliding thrust and significantly reduces the magnitude of active earth pressure. (2) The optimal inclination angle for the load transfer plate should be approximately 15°, with a recommended range of 10° to 20°. (3) At a 15° inclination, the theoretical calculation of active earth pressure unloading efficiency for a single-layer plate is 43% to 46.4%, while the experimental measured data range from 73.5% to 84%. For double-layer plates, the theoretical calculation is 46.3% to 49%, and the experimental data range from 83.4% to 93.1%, demonstrating that multiple layers enhance unloading efficiency more effectively. (4) The installation of a load transfer plate structure in slope support engineering can effectively alter the direction of sliding thrust and significantly reduce active earth pressure. This study provides a scientific basis for the future design of novel plate-type support structures.