Abstract: FEM is proposed to solve the stress intensity factors of thermal fatigue crack networks are hard to solve, where those factors include several groups with two parallel cracks each and are due to the occurrence of shielding effect. The aim is to investigate the relationship between the shielding effect and the gap between cracks. The specific gap n, unshielded percentage s and crack length radio f of the thermal fatigue cracks are all defined, and it was found that the three factors are in a certain relationship with each other and irrelevant with the boundary condition and length of crack. The n-s-f relationship curves are given so that the stress intensity factor of the main crack can be deduced according to that of a single crack when the shielding effect occurs. Numerical example showed that the method proposed is correct and valid.