To enhance the uniformity of material removal for lithium tantalate (LiTaO₃, LT) wafers, a model based on the three-dimensional micro-cutting of abrasive particles was developed. The model starts by analyzing the brittle and plastic removal mechanisms of LiTaO₃ crystals, alongside the distribution of abrasive particles on the lapping pad. Using a force balance equation, it calculates the penetration depth and chip cross-section for each abrasive particle. A kinematic analysis subsequently derives the trajectory of these particles during double-sided lapping, leading to the establishment of the material removal uniformity model. Simulations were conducted to assess the effects of the speed ratios between the gear ring and the sun wheel (m) and between the gear ring and the lower plate (n) on material removal uniformity. Following this, experiments were performed on LiTaO₃ wafers, measuring the Total Thickness Variation (TTV) across different speed ratios m and n to validate the model. Results indicate that the uniformity of material removal is significantly influenced by these speed ratios, achieving optimal uniformity at m=0.85 and n=1.3, resulting in a TTV of 0.83 μm. The experimental findings align with the simulation, demonstrating the model's potential to guide improvements in the double-sided lapping uniformity of LiTaO₃ wafers.