The spectrometers are widely used in various fields ranging from astronomy to biology. Recently, lots of efforts have been made to miniaturize the size of the spectrometer to meet the needs of fields such as real-time health monitoring. Therefore, achieving a high-resolution, broadband on-chip spectrometer is an intriguing but challenging topic. Photonic crystals are constructed by material with periodic refractive indices. They allow us to modify the interaction between electromagnetic fields and dielectric media. In this work, using a special kind of photonic crystal called “zipper cavity”, we design a wavelength tunable filter, which can be used as the key component for a filter-based spectrometer. By FEM simulation, we design a zipper cavity with a resolution of sub-nanometer and a wavelength tunable range of 21 nm. The prototypes of the devices are fabricated and measured. The loss rate is evaluated and the tunability of the wavelength is examined.