Terahertz (THz) metasurface sensing has attracted much attention in the field of highly sensitive biosensor due to its unique advantages of non-invasive and label-free detection. However, the existing techniques is still limited by low sensing sensitivity. Here we proposed a metasurface biosensor based on bound states in the continuum (BIC) for achieving highly sensitive detection of analytes. The metasurface consists of two metal open-ring resonators with opposite openings. By breaking the C2 symmetry of the metal resonators, the non-radiating BIC state can be tuned into Fano shaped q-BIC resonance with an ultra-high quality factor, which can greatly enhance light-analyte interaction. The designed metasurface shows a sensing sensitivity of 326 GHz/RIU, which significantly improves the use of THz biomolecular sensing technology for detecting low-concentration analytes.