An approach extracting information of both optical monitoring signal and phase thickness of deposited layer on a trace diagram is proposed. Realtime fitting and calculation are performed to get both practical thickness and refractive index of deposited layer with the assist of quartz crystal monitoring for keeping steady rate of deposition. Monitoring error of thickness using this approach is analyzed. It was used to obtain the refractive indices and thickness of Ge layer and SiO layer in in situ measurement mode, and the results were compared with those of ex-situ spectral measurement using infrared spectrometer. The effectiveness of the proposed monitoring method was verified by fabricating narrow bandpass filter consisting of quarter-wave and non-quarter-wave layers.