Biosensor has received increasing attention in recent years due to the demand for detecting biological and chemical substances in liquid. In particular, the detection methods based on refractive index have advantages in detection sensitivity. Colorimetric biosensor can transform the change in refractive index of target into the change in color, which has advantages in simple operation, low cost and real-time detection with naked human eyes. In this work, a Fabry-Pérot cavity colorimetric biosensor based on α-MoO ₃integrating microfluidic channel is proposed. The α-MoO ₃is an emerging natural two-dimensional van der Waals material with anisotropic optical properties due to its unique crystal structure. Theoretical analysis of the feasibility of BK7/Ag/SiO ₂as the reflective layers is carried out. And the transmittance spectra of the proposed colorimetric biosensor are calculated by the transfer-matrix method. The obvious color changes can be observed when the microfluidic channel filled with NaCl solutions with different concentrations. The proposed colorimetric biosensor achieves a high detection sensitivity of 600 nm/RIU, which can detect a concentration change of NaCl solution as low as 9‰. The proposed colorimetric biosensor can tune the operating wavelength by simply rotating the device due to the anisotropic optical properties of α-MoO ₃to satisfy the color vision of human eyes. Moreover, by tuning the thickness of microfluidic channel, the operating wavelength of colorimetric biosensor can be further shifted. Our approach offers a new direction for developing tunable biosensors with low cost and real-time detection.