Abstract: An improved design of ultra-wideband band-pass filter is presented in this paper.By this design,we can effectively expand the stop-band to achieve harmonic suppression.The filter is based on the coupling structure of microstrip and CPW.In the filter,the microstrip and the CPW are at the different side of the substrate.An improved CPW low-pass structure is arranged on the input/output of the filter in order to suppress the harmonic in the high frequency and achieve good performance in both pass-band and stop-band.The configuration and the performance of the filter obtained in both simulation and measurement are presented.Both of the results show that the UWB band-pass filter has a good performance in harmonic suppression,and it make the upper stop-band up to 20.0GHz,almost three times of the center frequency.