In order to realize a reliable and optimum mooring system, it is essential to estimate the behavior of anchors at the mooring site. But, the information about the performance of anchor is very poor in regard to various type of soil. At the same time, it is not uncommon that the mechanical characteristics of sea bed soil are not known over the anchorage. This paper introduces two indexes, the Holding Index and the Anchor Index , to evaluate the maximum holding power of anchor at the mooring site. The former which represents the condition of sea bed soil is measured at the mooring site as the holding power of the standard sounding anchor . The Anchor Index which represents the performance of an anchor is defind as the ratio of its maximum holding power to that of the standard sounding anchor. The maximum holding power of a bower anchor in any dimension can be calculated on the basis of these indexes. Trials of five types of anchor were conducted at three sites in order to determine anchor indexes and to make a map of holding index. It is also shown that the mechanical characteristics of sea bed soil in a bay varies considerably in short range.