A tunable thin-film filter of multi-channel based on thermo-optic is designed. The filer is made of amorphous silicon and silicon nitride layers grown by PECVD. Multiple-channel filer is obtained by designing the structure of the cavity. Due to the excellent thermo-optical property of a-Si, the refractive index of the cavity will be changed by heating; the filter's peaks wavelength and the width between adjacent routeways will therefore shift substantially. The tuning range is >17nm and the tuning coefficient (dλ/dT) is 0.085nm/K.