The promising prospect of a terahertz metasurface in sensing and detection applications has attracted increasing attention because of its ability to overcome the classical diffraction limit and the enhancement of field intensity. In this work, a novel scheme based on an all-silicon terahertz plasmon metasurface is proposed and experimentally demonstrated to be a highly sensitive biosensor for the Bacillus thuringiensis Cry1Ac toxin. The regression coefficients between Bacillus thuringiensis protein concentrations and the spectral resonance intensity and frequency were 0.8988 and 0.9238, respectively. The resonance amplitude variation and frequency shift of the metasurface were investigated in terms of both thickness and permittivity change of the analyte, which reflected the protein residue in the actual process. Moreover, the reliability and stability of the metasurface chip were verified by time period, temperature, and humidity control. These results promise the ability of the proposed metasurface chip as a Bacillus thuringiensis protein sensor with high sensitivity and stability. In addition, this novel device strategy provides opportunities for the advancement of terahertz functional applications in the fields of biochemical sensing and detection.