Abstract: The Crossing cracks were found in B position of 30% steel-casting side frame at foundry. Analysis was performed on the crack zone by chemical compositions ,macroscopic and microscopic testing. The results showed that gear axle failure resulted from hydrogen brittleness and fatigue fracture. Foundry pouring and moulding procedure were casted back,and technics was improved and supervised. The result showed that crossing crack in B position was caused preventing crack tie bar designing mistakenly. And the improved methods were put forward.