Abstract: The measurement and judgment for the geometrical characteristics of satellite clusters are required in the earth-observing missions of satellites constellation or formation.The concepts and definitions of mean angular separation and subpoints distribution area are introduced.These quantities are used to characterize the spherical geometry of subpoints.The mean angular separation can be formulated by reference orbital elements as a one-dimensioned measure of subpoints distribution.An algorithm of determining the minimum convex spherical polygon is presented.Using the algorithm,the geometrical distribution of all subpoints can be achieved without calculating the subpoint coordinates,as a departure from the classical algorithm.Furthermore,the distribution area can be obtained as a two-dimensional measure of subpoint geometry property.The presented approach is exemplified to determine the spherical geometrical characteristics of a formation of four-satellites.The correlation between the reference orbital elements and the distribution area are analyzed in a semi-quantitative manner.