The electromagnetic distribution in hollow fiber always is one of key research points of hollow waveguide. Under certain hypotheses, the energy distribution of output laser passed through hollow waveguide seems to reflect the electromagnetic distribution in hollow fiber, but the conventional measurement approaches are much complex and the device is too expensive. A simple and effective method for measuring the energy distribution and its applications on mode purity analysis and coupling status detection of hollow waveguide are introduced in this paper. Finally, the output beam waist problem for a beam passing through a hollow fiber is discussed and the output beam focus of different hollow fibers is measured.