The invention provides a visual detection method and system for GTAW additive manufacturing stack height for image processing. The axis of a CCD camera is vertical to a plane formed by the axis of a GTAW welding gun and a threaded tube. The method comprises the following steps of: starting continuous image collection to calibrate a sensing system so as to determine the position of a tip of a tungsten electrode; determining the initial distance from the tip of the tungsten electrode to the surface of a substrate, and starting a GTAW electric arc and filler rod system; extracting surface characteristics of the tail of a weld pool of a deposition layer by means of a picture processing algorithm; calculating the mean square error of row-coordinates on the surface of the weld pool of the deposition layer of a corresponding row of adjacent continuous images, and determining the junction point of liquid and solid metals at the tail of the weld pool of the deposition layer by means of a threshold value method; and when the nth layer is stacked, calculating the total height of the deposition layer at the current moment according to the initial distance from the tip of the tungsten electrode to the surface of the substrate, the tip position of the tungsten electrode and the junction point of liquid and solid metals of the deposition layer. The method provided by the invention solves the problem that the GTAW additive manufacturing stack height is hard to detect in real time effectively, and has the advantages of being simple in detection process and intuitive and rich in amount of information.