A method for treating mixed wastewater from pharmaceutical chemical industry parks including introducing mixed wastewater into a regulation tank for regulation of water flow and water quality, and then into a hydrolysis tank having a hanged filler and employing upflow water distribution, into an anaerobic tank employing upflow water distribution, into a moving bed biofilm reactor having a suspended filler and an aeration device at the bottom thereof, into a biological aerated filter including a ceramic filler, and finally treating using coagulating precipitation process. The final effluent has less than 100 mg/L COD.