Abstract: Using the Polar Satellites IR data in 182 days during the summers of 1998～2000 over Tibetan Plateau, 28685 Mesoscale Convective Systems(MCSS) and some factors of their feature during their initiation, such as daily freguency, intensity, shape, daily variation and geographic distribution, were automatically and objectively tracked and extracted by computer. The results show that the daily mean number of MCSS was 163 of which 76% was only several hundreds km² and 4% of them was>10⁴km². Most of them were band, comma and other irregular types and about 30% of them belonged to circular and ellipse types. The mean minimum temperature at the cloud top was around 51 ℃. MCS number in the early afternoon was over twice that in the early morning and the number of MCSS with T_BB≤54 ℃ was five times as many. The MCSS initiating area occarred mainly over the Plateau south of 33°N where two active regions were over Yaluzangbu River basin and the western Sichuan province to Hengduan Mountain, respectively, and which shows that strong monsoon activity plays a main role in MCS initiation.