Loaded tooth contact analysis (LTCA) adopted to obtain the static transmission error for the gear optimization affects significantly the computation time and results. This paper is to study an efficient process of macro geometry optimization of helical gear pairs with LTCA. An analytical LTCA model was proposed and verified with the measured transmission error. To find an efficient LTCA method, the proposed model was divided into three types (based on whether the slice stiffness and extended contact were included) by adjusting the fidelity. When extended contact was included in LTCA, the increased computation time was very short, but the accuracy of the results improved significantly. Optimization processes were designed based on the analysis results, and it was most efficient when starting with the model considering only the extended contact and ending 5%−10% of the entire generation with the highest fidelity model. In the process, the computational effort was significantly reduced compared to when the optimization process was configured with only the highest fidelity model, and the level of optimization was almost equal.