Propagation constant and field evolution in the tapered region are discussed using numerical method based on waveguide theory.GNSE is resolved by the split-step Fourier method to study the transmission characteristics of ultra-short pulse in the tapered region.The calculated results show that at the beginning of the tapered fiber,propagation constant decreases gradually while in the end it drops dramatically.After the “transition point”,energy redistributes in the fiber,and it becomes very large in the end.It is found that pulse width is broadened along the tapered region when the pulse width is smaller than 80fs.