In order to ensure the biochemical treated water (also known as the reclaimed water) can be safely used in agricultural irrigation, a model predictive controlmethod is used for effective control of dissolved oxygen in the activated sludge biological wastewater treatment process. In generally, maintaining the dissolved oxygen concentration around 2 mg/ L willmake the activated sludge process effectively for organic pollutants removing. Simulation results under Benchmark show that the model predictive control method is better than conventional PI control method in terms of response speed, overshoot and other performance. Stable and reliable treatment process is the assurance of high quality reclaimed water out from the wastewater treatment plants, and the reclaimed water will be more suitable for agricultural irrigation. Theworks have important practical guiding significance.