Tetracycline hydrochloride (TC) is a typical refractory organic pollutant, and is frequently detected in different water environments, which will increase microbial drug resistance, destroy ecosystems and threaten human health. It is urgent to develop a simple and effective catalyst for TC removal. In this paper, a facile two-step calcination method was used to prepare a LaCoO₃/g-C₃N₄ composite catalyst with high activity and high stability for PMS activation to degrade TC. Various characterization results confirmed that the LaCoO₃/g-C₃N₄ composite catalyst possessed smaller particle size, higher stability and faster electronic transmission ability. Benefiting from the synergistic effect between LaCoO₃ and g-C₃N₄, the LaCoO₃/g-C₃N₄ catalyst showed high activity for PMS activation to degrade different antibiotics. Furthermore, the results of the quenching experiments and the electron paramagnetic resonance (EPR) tests showed that the generated SO₄˙⁻ and ¹O₂ radicals during the PMS activation process played a key role in pollutant degradation. The effect of different reaction conditions (including pH, temperature, PMS concentration, catalyst dosage and different anions) on the performance of the catalyst was also investigated. The catalyst cycle evaluation experiments showed that the LaCoO₃/g-C₃N₄ composite catalyst has high stability and reusability. The phytotoxicity evaluation based on seed germination experiments indicated that the LaCoO₃/g-C₃N₄ composite catalyst system can effectively reduce the toxicity of antibiotics.