Effectively optimizing the design process of a wastewater treatment plant to achieve higher pollutant removal rates is extremely time-consuming, and digital model simulations are an effective way to optimize the operational performance of an existing wastewater treatment plant. This study takes the oxidation channel treatment process at Guishan wastewater treatment plant as an example and uses GPS-X wastewater treatment system simulation software to simulate improvement scenarios. Five scenarios were simulated, including scenario A: increased flow rate, scenario B: increased aeration in oxidation ditches, scenario C: returned flow from the secondary settling tanks to the anoxic sections of oxidation ditches, scenario D: a combination of scenarios A + B, and scenario E: a combination of scenarios A + B + C. The simulation results revealed that among the five scenarios, scenario E exhibited the most significant improvement in ammonia nitrogen and total nitrogen removal rates. Under scenario E, the ammonia nitrogen removal rate increased from 36.4–95.0%, and the total nitrogen removal rate increased from 50.5–86.3%.