An attachment part of the construction equipment frequently claimed from the crack occurrence that takes especially at the bucket. therefore we execute the fatigue examination and changes the welding method at the same materials. we executed a fatigue crack propagation experiment and got the conclusions at the normal temperature and Frequency 10Hz. We carried out butt welding for structure steel of SM490A and make three kinds of specimen of different weld method each. The fatigue limit of CASE 1 was determined to the low than CASE 2, CASE 3. the CASE 2 putting the interval of the 2mm creates back plate and make fatigue limit to high. Bead shapes and weld surfaces shape influence on fatigue life of materials. Specially, the crack growth becomes starting point that gap of back-plate and boundary surface of bead. It is confirmed by fracture showing on this study.