Based on the NCEP reanalysis, FY-2 satellite TBB and rainfall data from automatic precipitation stations etc., the two cold front shear processes which occurred in Yunnan on July 2 and 5, 2008 were analyzed. The results show that the cold front shear, range and rainfall between two processes are distinctly different, and that the intensity and movement of cold front sheer affect the intensity of rainfall. Meanwhile, the generation and maintaining of mesoscale system originated in sheer line significantly influence the intensity of rainfall. The YunnanBurma high ridge, plays an important role in vapor transport and convergence. The rainfall intensity differences result in the differences of strength of convection development during two convection processes, and thermal instablility indexes such as pseudoequivalent potential temperature, K index, total energy, CAPE, etc. Could reflect the differences of development of convection. Different conditions lead to different changes of physical fields, which is the main reason for intensity changes of precipitation occurring in cold front sheer system.