In order to solve the challenge of freeform surface measurement, a large-range laser differential confocal sensor with high precision was constructed. Based on the principle of laser differential confocal focusing, the sensor uses normalized single-point focusing model to eliminate the influences of the surface reflectivity and tilt of the capsule. A non-equidistant fractional-order accumulation model is used to predict the focus position and achieve fast tracking and focusing. The aerostatic linear guideway and PZT are combined to expand the axial scanning range. The experiment results show that the axial resolution of the sensor is better than 3nm and the measured surface tilt angle can reach 22°. The axial scanning range can reach 50mm and the zero-crossing standard deviation of the differential curve is 5.7nm, which has good repeatability. The sensor provides a new method for measuring the profile of freeform surface.