Although improvements in ultrasonic inspection methods have brought about a reduction in the incidence of alumino-thermic weld failure, some failures still occur in the early stages after installation of weld as a result of solidification cracks. It is considered that such cracks arise from rail movement in the longitudinal direction just before the weld metal solidifies. However, the details of the related occurrence conditions are not yet clear. In this study, the occurrence conditions of solidification cracking and preventive methods for weld failures caused by such cracking were discussed based on simulative testing of solidification cracks. As a result, the occurrence conditions were clarified, and preventive methods and detective methods for solidification cracks were suggested.