Without properly treated wastewater released from the textile industry contains organic and inorganic pollutants that cause environmental problems like water body contamination, which causes marine life disappearance, soil contamination, and air pollution. Treatment of textile industry wastewater is difficult due to pollutant types existing like BOD, COD, toxic heavy metals, organic particle matter, inorganic particle matter, color, etc. The multi-component wastewater pollutant needs proper designs to remove such pollutants. Dire Dawa textile wastewater treatment plant (design) and simulation was the objective of this study. The method of this study was experimental and software modelling. STOAT model software is the best capable of simulation treatments plants, and the time to complete the simulation was 3 days. The STOAT graphic and statically data analysis model efficiently removed the multi-components of pollutants effluent from Dire Dawa textile industry. Some pollutant parameter measures before design model are SS 350 mg/L, DS 2000 mg/L, ammonia 55 mg/L, BOD 350 mg/L, nitrate 0 mg/L and DO 12 mg/L. The effluent of wastewater treatment plant model simulation results are 2 mg/L SS, ammonia 8.82 mg/L, BOD 2.5 mg/L, and nitrate increases from 0 to 58 mg/L by ammonia oxidation. Totally 98.7% SS, 99% BOD, and 84% ammonia were removed in the design model. In the sludge outlet, nitrate contents increase due to nitrification being processed rather than denitrification.