The energy loss of fiber tapered is an important problem in research of Near-Field Optical disc technique. To calculate accurately energy loss, laser waveguide model in fiber tapered should be made. The paper discusses the problem of waveguide of fiber tapered with three layers medium (core, clad and air). The paper makes a model that transforms waveguide problem to problem of a series equation. If boundary condition is confirmed, numerical solution of waveguide in fiber tapered can be got by using the model. In the condition of column-symmetry field the paper provides an example.