We proposed a high-Q in-plane channel drop filter using photonic crystal (PhC) cavities that are defined by an effective Aubry-André-Harper (AAH) bichromatic potential. The channel drop filter consists of AAH cavities and line-defect waveguides. Three-port structure with a wavelength-selective reflection cavity is applied. The parameters of the channel drop filter is analyzed by two-dimensional (2D) finite-difference-time-domain (FDTD) method. The simulation results are namely, the center wavelength of the filter being 1573.0 nm, and the insertion loss being smaller than 0.6 dB. The 3 dB bandwidth is 0.2 nm, and the loaded Q is up to 8×10<sup>3</sup>. So the proposed device can be applied in a dense wavelength division multiplexing (DWDM) system with a 100 GHz channel spacing. Besides, the channel drop filter has a broad free spectral range (FSR) of around 250 nm, covering from 1350 nm to 1600 nm. The footprint of the channel drop filter unit is only 10 μm×20 μm.