In order to reveal the characteristics of the dynamics, thermal dynamics and the water vapor, cloud system and precipitation characteristics for plateau shear lines and to further understand the evolution mechanism of shear line, the evolution characteristics and effects on precipitation of the plateau shear line in different times and at different development stages have been analyzed by selecting three cases of plateau shear line that occurred on 19-22 May 2008, on 1-3 July 2007 and on 19-21 September 2009 respectively as well as adopting MICAPS data, NCEP 1°×1° reanalysis data, FY-infrared temperature data, etc. The results show that: (1) While winds on both sides of the shear line weaken, especially north wind, the shear line process tends to weaken. The strength of cold and warm air affects the position of shear line. Shear lines in early summer and midsummer are northerly situated while those in late summer are southerly situated. (2) During shear line process, there is positive vorticity, convergence and ascent movement in coordination with the shear line. While the shear line is disappearing, the convergence belts weaken ahead of the positive vorticity belts. There are multi centres of positive vorticity and convergence around the shear line, which may be relative to the plateau vortex activities. The characteristics of positive vorticity centers moving eastwards are obvious for midsummer and late summer shear lines, and the convergence ascent areas are more eastern situated and the motion is stronger than that for early summer shear line. (3) There are band areas or block areas of TBB<-20℃ nearby the shear line. During the shear line maintaining, TBB values further reduce. There are multi-centers of TBB low values for midsummer shear line at maintaining stage and late summer shear line at initial stage, which shows that convective activities are stronger. (4) The east and south slopes of the plateau are areas with congregated unstable energies due to terrain blocking and heating. The characteristics of high temperature and high humidity energy are obvious in near-surface layer around the shear line in midsummer. Early summer shear line brings about stable and small precipitation which is in patch form while the characteristics of unstable convective precipitation are obvious for midsummer and late summer shear lines. The distribution of precipitation, which is in band form around the shear line, is larger and intensities are stronger. (5) The shear lines on 500 hPa are also water vapour congregated band. The conglomeration of vapor and instability energies, and positive vorticity transmitting eastward and convection developing over the shear line are important mechanisms that lead to heavy precipitation.