Abstract: By taking a die for forming connecting iron as an example, the importance to the strength calculation of die design for high density and irregular shape parts has been outlined.The real reason of die cracks is that the strength is insufficient The correct way for design improvement is to choose proper materials. The steel with higher strength should be used.Alloying steel (modified 40Cr or bearing steel GCr15) is better than carbon steel (45^# steel) for making die sleeves.