Based on equivalent LC resonant circuit, the response between the resonance frequency and the electric parameters of the equivalent circuit were analyzed. Different from the traditional transmission line loaded with split-ring resonator structure, two different split-ring resonator structures were designed as the transmission medium. In consequence, two passband filters are achieved in this paper which bandwidth are 300 MHz and 200 MHz with square and circular split-ring resonator respectively, by loading with varactor and bias circuit in the split-ring resonator structure, two continuous tunable passband filters are finished in the end. The difference in surface current density between the square and circular split-ring resonator is given in this paper, the transmission coefficient of the square split-ring resonator is 3dB higher than the circulal’s within the passband, analysis shows the effective distance is one of important reason for the coupling efficiency.