The propagation direction of a surface crack in tubular T-joints and the surface crack profile are studied in this paper. By using Photoelasticity and Finite Element method, the distribution of Stress Intensity Factor (SIF) along the front edge of the prefabricated semi-elliptic surface cracks at the hot spots of tubular T-joints is obtained. The results show that the cracks are subjected to mix-mode loading, and the distribution of SIF along the front edge of the crack depends not only on aT, the ratio of crack depth to the thickness of chord wall, but also largely on shape ratio ac, the ratio of depth of the cracka to its length c. It can also be predicted that there exists a certain precedent propagation direction for a surface crack with a certain ac. According to the Strain Energy Density Factor theory the condition of constant strain energy density factor S on the front edge of the crack will be enforced on each point of the prospective crack profile, so that the crack profile can be pre-estimated.