In order to optimize bolt locations for suspension joint parts of a GFRP composite bogie frame, the optimum design was done. The structural integrity of a composite bogie frame was evaluated under three main in-service loads according to JISE 4207. The optimum design was conducted using a sub-modeling technique, a sub-problem approximation method, and batch processing codes programmed by ANSYS Parametric Design Language (APDL). The results showed that the optimum design using the sub-modeling technique was able to obtain more accurate results by the control of mesh density for the interesting parts, and reduce maximum Von-Mises stress in comparison with initial model.