As planar eight-bar linkages can achieve a more complex kinematic trajectory curve and satisfy the needs of practical applications better in the field of agricultural machinery, an automatic generation method for determining the crank existence region of an eight-bar linkage with a six-bar group was hereby proposed. Compared with the direct solution method of position equations, the numerical iteration solution of the type transformation method (NISTTM) was proved to be more simple in solution programme and more effective in solution time: firstly, all possible initial position solutions of the linkage were solved based on NISTTM;then, based on each initial position solution, NISTTM was also adopted for kinematic analysis, effectively avoiding the problem of higher-order nonlinear equations failing to determine the optimal solution for multiple solutions;finally, the loop without branch defects was screened by using the Jacobian matrix method. The crank can exist in the loop when the position solutions of the linkage can be obtained for the whole rotation cycle of the driving link. Based on the above theoretical basis, the crank existence region of an eight-bar linkage with a six-bar group could be automatically generated in the given region by a VC++ program combined with OpenGL. The numerical example justified the simplicity, effectiveness, and practicability of this method, which can help the designer master the distribution of the crank existence region and be guided to complete the analysis task with no difficulty quickly.