A novel three-port band-pass tunable filter based on DWDM angle-tuned thin-film filter was proposed.The tunable filter consists of three single-fiber collimators and one particular designed angle-tuned narrowband multiple cavities thin film filter.By the controlling of a stepping motor,the tunable filter can choose any particular wavelength to the drop port,and reflected wavelengths can go out from another port without any interrupt.With the theoretical calculation and the experiment research,the characteristics of the three-port tunable filter was analyzed,especially the crosstalk was calculated in detail.In the experiment,the channel isolation was at about 30dB and its tunable range was over 26 nm,which was coinciding with the result of theoretical design.