Abstract: Tetracycline is currently the most predominant antibiotic pollutant, and photocatalytic technology holds extensive prospects in the domain of pollution remediation. The catalyst g-C₃N₄ has emerged as a research focus in the realm of photocatalytic degradation of tetracycline on account of its merits, including simple preparation, excellent stability, and favorable light responsiveness. However, limitations such as small specific surface area and high charge recombination ratio have limited its practical application. In this study, we prepared a two-phase composite material of g-C₃N₄/C. by introducing dandelion stem as a biological template and melamine as a precursor, we then uniformly load ZnSe on the surface of the biological carbon via a hydrothermal method. An II-type heterojunction was constructed between ZnSe and g-C₃N₄, leading to the preparation of the ZnSe-g-C₃N₄/C three-phase composite material. After the photocatalytic performance test, the degradation rate of tetracycline of 30%ZnSe-g-C₃N₄/C material with the best performance reached 57.7% after irradiation under 500 W xenon lamp for 1 h. This rate is twice that of the pure-phase g-C₃N₄ and 7.7% higher than that of the two-phase material. Additionally, its tetracycline degradation rate decreased by only 1.1% after four cycles, demonstrating excellent photocatalytic stability. The introduction of biological carbon increased the specific surface area of the composite and was conducive to the transmission of photogenerated carriers. The II-type heterojunction between ZnSe and g-C₃N₄ reduced the charge recombination ratio, and the synergistic effect was enhanced between single phase material, thus enhancing the overall photocatalytic performance.