Based on the theory of the general Chebyshev band pass filter with finite transmission zeros, the simulation model of the filter has been designed according to the calculated couple matrix. The size of the duplexer has been optimized by using the group delay fitting method and combining EM simulation software with a optimal method. The test results shows that the designed duplexer has the insertion loss of equal to or less than 1.5 dB, VSWR of equal to or less than 1.5 and the band stop rejection of greater than 85 dB. The obtained curves agree well with the design specifications, indicating that this method is correct.