A significant amount of wastewater containing fine catalyst particles is produced in the methanol-to-olefin (MTO) process, which restricts the long-period operation of the processing unit. To address this key problem, a minihydrocyclone was designed for MTO wastewater treatment and tested in the laboratory. Good separation performance and a small cut diameter were achieved under certain feed conditions. Furthermore, a group composed of 300 parallel-arranged minihydrocyclones was applied to the industrial unit in the MTO quench water treatment. The obtained results indicated that the separation efficiency and precision of the minihydrocyclone can meet the requirements of fine catalyst particle separation, and the designed minihydrocyclone group with reasonable parallel configuration exerted an outstanding application effect on the treatment of MTO quench water.