Bi12O15Cl6/g-C3N4 binary type Ⅱ heterojunction photocatalyst was prepared by wet impregnation method. The crystal structure, morphology, and optical absorption of the samples were characterized by XRD, SEM, and UV-vis diffuse reflectance spectroscopy. With tetracycline as the target pollutant, the effects of doping ratio, dosage, and initial solution concentration on the photocatalytic degradation of Bi12O15Cl6/g-C3N4 were investigated under visible light. The results show that the removal rate of tetracycline is 96.43% in visible light irradiation for 150 min when the doping ratio is 50%, the dosage is 1.6 g/L, and the initial concentration of the solution is 10 mg/L. Finally, through the free radical capture experiment, it was proved that the free radicals playing the main role in the process of photocatalysis are h+ and ·O-2.