In order to obtain a final sound product by the incremental sheet forming (ISF) process for complex shape using cold rolled steel material, the limit curve based on the maximum wall angle versus maximum deformed height was established utilizing finite element method (FEM) simulations for several square shapes with various wall angles. The forming limit diagram (FLD) obtained from modified maximum force criterion (MMFC) was first used to predict ductile fracture of ISF simulation test and shown the inaccuracy when comparing with corresponding experimental results. The FLC at fracture (FLCF) curve regarding to tool dimension effects was then proposed, inputted to FEM simulation and approved in good agreement with experiment results. After that wall angle of square shapes was changed to verify its effect on fracture height of the square shapes and obtain the forming limit curve. Finally, wall angles with corresponding maximum deformed height of complex shapes were put into the obtained forming limit to investigate "fail" or "safe" shapes and validated by corresponding experiments.