Abstract: Stress intensity factors of slanted thermal fatigue cracking and the periodic change patterns of cracking growth angle were calculated using the finite element method (FEM) and maximum tangential stress criterion. During the heating process, thermal compression stress was generated inside the model causing squeezing and staggering between the two crack faces. Due to the fact that deformation caused by heat-induced compression plasticity was not freely reversible, tensile stress generated during the latter part of the cooling process made the crack open. Slanted thermal fatigue cracking during the heating process and during the initial part of the cooling process was entirely mode II, and KII reached maximum as the heating process finished; a I-II mixed mode occurred during the latter part of the cooling process. Both KI and Ke maximized at the end of cooling period, and cracking growth was most prevalent this period.