Chromatic Confocal Displacement Sensor (CCDS) is now used widely for its high precise and robust property. As the key component, the objective is used to achieve longitudinal focus vibration with wavelength. The theory of CCDS is analyzed and formulae for calculating the parameters of objective are presented. With the formulae guiding, a dispersive objective was designed. To obtain large axial aberration, the objective is configured with high dispersive glass singlet and special doublet lens. And aplanatic lenses and doublet are used to reduce longitudinal aberration. The objective dispersed the focus of wavelength between 500~700 nm to 1 mm longitudinal range, and the longitudinal aberration is less than 0.6 μm. With selected spectrometer, the resolution of CCDS is no more than 1 μm, which meets the requirements of dispersive objective precision.