Dispersive objective is the key component of Chromatic Confocal Microscope (CCM). The measuring range of CCM depends on the chromatic aberration of dispersive objective, and the nonlinear axial chromatic aberration of dispersive objective would lower the sensitivity of CCM. To achieve large axial chromatic aberration, optimization method of selecting materials combination is proposed based on the principle of linear axial chromatic aberration. The optimization model is presented and solved to get the optimal solutions, which are the materials combinations of largest linear axial chromatic aberration. The results from optical design software indicate that lenses of optimal materials combinations could achieve largest linear axial chromatic aberration among the glass catalog. With the optimal materials combination, a dispersive objective was designed for CCM. The well designed objective could provide large linear measuring range while having a short tube length. Optimization and selection of materials are significant for dispersive objective design to heighten the performance of CCM.