Abstract: Area navigation capacity is an important parameter for evaluating navigation performance of constellation.The evaluation indexes of area navigation capability were presented,including standard deviation of geometry dilute of precision and variability of geometry dilute of precision from geometry dilute of precision,and the key-satellite of the navigation constellation was analyzed based on the indexes.The two indexes and area average geometry dilute of precision describe the area navigation capability in different ways.The indexes can fulfill different applications for determining the key-satellite of constellation for area navigation.The correlations between these indexes insure that the key-satellite is the same one in most cases.