According to transmission matrix method, the transmission characteristics of series coupled dual micro-ring resonator filter are analyzed. The transmission function formula, the best coupling conditions of channels and drop channels are deduced. At the condition of neglecting loss, the influence of coupling coefficients and micro-ring radius on filtering characteristics is calculated and analyzed. And parameters are optimized. The calculation results show that when the radius are 40 μm and 50 μm, the coupling coefficient of micro-ring and line waveguide is 0.2, the free spectral range of the filter is 22 nm and 3dB bandwidth is just 0.27 nm, therefore, only a special wavelength is filtered in dense wave division multiplex (DWDM) system with 50 GHZ internal.