For the fatigue design of a large scaled welded structure, the readily accessibility of various engineering tools is required for the static, fatigue, dynamic analysis and parametric study. In this paper, a multi-agent system is suggested for the development of distributed, open and intelligent design system. The developed design system is applied to assess cumulative fatigue damage on the welded bogie frame of railway vehicles. The engineering tools for fatigue durability analysis are chosen as I-DEAS, ANSYS and BFAP, in which iterative analysis is performed automatically caused by geometrical changes of transom support bracket attached in the bogie frame. The prototype of design system is implemented successfully for the assessment of cumulative fatigue damages of the welded bogie frame.