In order to achieve accurate and efficient non-contact measurement of curvature surface profile, a single-axis normal-tracking measuring method based on differential confocal principle is proposed, which has high resolution and signal-to-noise ratio.The factors that affect the system resolution are analyzed.The influence of tilt on differential confocal detection is studied wh en the incident light is a Gaussian beam.The optimal pinhole offset and pinhole size ar e verified by theoretical model and experiment when beam is tilted.The sensing s ystem is established,the working principle and structure of the system are introduced,and the experiments show that the sys tem can track the measured surface well,and the axial resolution of the system i s better than 5nm.The system can be used for large curvature surface contour measurement when combined with a high precision laser interferometry system.