Abstract: Means of optical emission spectrometer,microhardness tester,optical microscope,scanning electronic microscope were used to analyze craking reason of the failure spring seat.The results showed that the cracked spring seat was under tempering,which resulted in the high hardness and brittleness of the material.Inclusions and banded carbides level were both high and made the homogeneity of microstructure and properties became worse and stress concentration were formed at micro-region.Grinding cracks were produced because of the improper grinding process.In addition,the spring seat was assembled by strock methods and the force was difficult to controll.All above factors coacted and caused the spring seat cracked from the grinding cracks with serious stress concentration.Improvement measures were proposed and remarkable results were achieved.