The exploration of nanomaterials with mimic enzyme activity (named as nanozyme) has gained extensive attentions in the fields of advance analytical chemistry and material science. Herein, the gold nanoparticles-doped covalent organic frameworks (COFs) were prepared, which exhibited not only the excellent mimic nitroreductase activity but also robust stability. By replacing the traditional natural enzyme tag in enzyme-linked immunosorbent assay (ELISA), we employed the proposed nanozyme to label the detecting antibody. According to the catalytic properties of the nanozyme, 4-nitrothiophenol (4-NTP) was introduced as the substrate, which can be transformed to 4-aminothiophenol (4-ATP) in the presence of NaBH4. In SERS assay, 4-ATP was capable of functioning as a powerful bridge to connect the gold nanostars (with excellent SERS performance) by both Au-S bond and electrostatic force to further produce Raman "hot spot". Meanwhile, the Raman signal of 4-nitrothiophenol at 1573 cm-1 was weakened, and a new signal at 1591 cm-1 generated by 4-ATP was turned on, leading to the generation of ratiometric SERS signal. Based on this performance, a ratiometric nanozyme-linked immunosorbent assay (NELISA) strategy was developed delicately, which was applied to detect β-lactoglobulin (allergenic protein) by monitoring the ratiometric signal of I1591/I1573 with a limit of detection (LOD) of 0.01 ng/mL. The linear range is 25.65-6.2×104 ng/mL, covering more than three orders of magnitude. The developed method showed many advantages such as low-cost, higher recovery and lower cross-reactivity, providing a new insight on the application of SERS technology for trace target analysis.