Abstract: Microscopic structure of three kinds of stress cracks(single,double ,multiple) in corn was observed.The location,size,number and extension of stress cracks in endosperm were analyzed.For different grain kernels,the form,number and size of stress cracks are different.Stress cracks originate at the inner corn of the floury endosperm and propagate radically outward along the boundary of starch granules， they cannot advance enough to rip the pericarp,and only reach to the area closing to aleurone layer.