Abstract: Using the parameter of temperature and humidity inversed by Atmospheric Infrared Sounding(AIRS) and according to the formula of convective index that has been revised based on trait of the plateau,we have analyzed the Mesoscale Convective Systems(MCSs) in an heavy rainfall process happened in southeast of Tibetan Plateau on May 3 to 5,2013.The result is that because of the advantage of the AIRS data that multi-product,high precision and high spatial resolution,it can make up for the shortage caused by serious deficiency of sounding data in Tibetan Plateau.The K index is characterized of variation from high to low,maximum convective stability index (BI) has the low center which moves towards low center of Black Body Temperature.The low value zone of Showalter Index (SI) tends to form before MCSs,approximately from 0 to 5℃.It illustrates that the atmosphere over the Tibetan Plateau is already unstable before the MCSs formation.It is favorable for the formation of strong convective weather.These three convective indexes all have the low area in the process of development of MCSs,but the low area is not misaligned,and presents three characteristics of change.These conclusions remind us to consider the convective index comprehensively,when using convective index as assistant information for analyzing and forecasting weather.