Based on mechanical equilibrium, a formula for calculating the compressive strengths of concrete short columns wrapped with fiber reinforced plastics (FRP) is deduced. The strains of FRP do not reach their limit while strengthened columns are damaged in many experimens. On account of the fact mentioned above, this study introduced an efficiency coefficient of fiber reinforced plastics, which revise the compressive strengths of strengthened columns, thus proposing a method for determining the compressive strengths of circular short columns wrapped with FRP. The theoretical results in this paper are compared with the test results obtained by Demers.