Abstract: On the basis of study on the effect laws of change of distance between the sensor and workpiece on induced current and voltage and study on method for signal acquisition and processing,a single-chip capacitive sensor applied for weld seam tracking system with a novel electrode structure is proposed. An automatic weld seam tracking system based on capacitive sensor is also developed in this paper. On the premise of considering temperature effect,the system extracts the deviation between welding torch and the welding groove center in real time using Differential Measuring Method proposed,and then achieves seam tracking by controlling actuators to rectify deviation. The experimental results indicate that the capacitive sensor can be applied for seam tracking of fillet weld with complex trajectories. The sensor has the characters of simple structure,high resolution and reliability,non-contact measurement and the capacity to work under hard conditions of high temperature,radiation and strong vibration,which provides a new direction for the study on seam tracking technology.