The chromatic confocal displacement sensor has good applicability in the measurement of the scratch depth of the locomotive wheel axle, and the dispersive objective is the key device that determines the detection range and resolution of the sensor. According to the detection requirements, combined with the chromatic confocal principle and linear dispersion conditions, an appropriate initial structure was selected. The Zemax optical design software optimized and analyzed the initial structure, and designed a high-linearity and short-conjugate dispersion lens. The measurement range is 1 mm, the operating spectral range is 400 nm~700 nm, and the spherical aberration of the lens is less than 1.7 μm. The axial displacement resolution of the system is 0.615 μm, the dispersion linearity determination coefficient R² is 0.997 5, and the conjugate distance is 104 mm, which makes the lens miniaturized and has the advantages of high resolution and high linearity.