According to the structure equivalent strength optimization theory, each cavity die layer's size and inter layer interference of the flat end combined cavity die were obtained by using the Lame formula. The stress situation of the combined cavity die influenced by the end angle, stage height and both of them were analyzed. According to the method of data fitting, the function relationship between the maximum equivalent stress and height difference and the end angle was contained. The result shows that in the same circumstances the staged oblique end cavity die has higher strength than the flat one.