Bismuth-rich oxyhalides are promising photocatalysts due to their special layered structure and adjustable band gap energy. In this work, a series of bismuth oxyiodides were fabricated by grinding-assisted calcination in the presence of thiourea, where grinding-induced mechanical force could accelerate the decomposition reaction and thiourea could prohibit the crystal particles from growing due to coordination action. The combined effect of grinding and thiourea could decrease the temperature of phase transformation of bismuth oxyiodides. Among these, heterojunction Bi4O5I2/Bi5O7I containing uniform flower-like microspheres assembled by ultra-thin nanosheets exhibited the highest photocatalytic activity and favorable stability for the degradation of the antibiotic tetracycline under visible light irradiation. This work could provide a good reference for the design of bismuth-rich oxyhalide heterojunction for photocatalytic applications.