By using the NCEP/NCAR monthly mean reanalysis data from 1948 to 1999，the characteristic indexes are defined to describe the Mascarene High (MH)， based on the evolution characteristics of the climatological geopotential height and streamline fields at 850 hPa. By calculating the indexes, the features of the MH variations on different time scales are examined. The results show that the seasonal variations of MH were remarkable: it was the strongest and the location is more westward and northward in southern winter, and vice versa in southern summer. The anomaly variations of MH are also studied. It is shown that MH had the obvious interannual and interdecadal variations. On the interdecadal time scale, the area and center intensity of MH increased gradually, and the center location moved eastward and southward slowly in 52 years.