Abstract: A circuit model for coaxial cavity filter constructed from negative sub networks is presented in this paper. Based on this model, circuit parameters such as cavity coupling factors and input output locations of are optimized by commercial microwave circuit simulation software. The width of coupling windows between the cavities and diameters of input output lines are acquired by modal frequency analysis and full wave optimization with commercial 3D full wave simulation software. A six cavity band pass filter with a pass band of 100MHz at 2.4GHz designed in this way has the response coincided with the result of circuit simulation.