In this work, a monomer-mediated in situ growth strategy was developed for the controllable construction of core-shell Co₃O₄@TAPB-DMTP−COF composite (TAPB, 1,3,5-tris(4-aminophenyl)benzene; DMTP, 2,5-dimethoxyterephaldehyde; COF, covalent organic framework), which exhibits uniform size, high surface area, outstanding thermochemical stability, and ultrahigh effective surface area. The Co₃O₄@TAPB-DMTP−COF was further applied to develop an electrochemical sensor for the sensitive and selective determination of tert-butylhydroquinone (TBHQ). Mechanism investigations reveal that multistacked columnar channels given by TAPB-DMTP−COF shell can effectively facilitate the diffusion of TBHQ molecules to the active Co³⁺ sites. Under the optimal conditions, the current response exhibits two linear dynamic ranges, 0.05−1.0 and 1.0−400 μmol L⁻¹, and the detection limit was as low as 0.02 μmol L⁻¹ (S/N = 3). Little to no interference effects from other co-existing ions allows the sensor to detect low-abundance TBHQ from complicated real samples. This study not only provides a strategy for crystalline and shape-tailored growth of COF shells, but also expands their further use in electrochemical sensor.