This paper presents an optimization of voice coil motor (VCM) used in ultra-precision motion stages based on an improved magnetic equivalent circuit (MEC) model. The modified MEC model takes into consideration the nonlinear saturation effect of ferromagnetic material by segmentation, and estimates the magnetic flux density in air gap of VCM in a more precise way. The results of experiment, finite-element analysis, and MEC model are compared to validate the correctness of the improved MEC method. A new optimization criterion is used to measure dynamic response and heat dissipation of VCM simultaneously. The geometric parameters of VCM are optimized, and the resulting VCM is proved to have a better dynamic response and lower heat dissipation.