Embodiments herein relate to methods for sludge reduction for pretreatment of nitrotoluene wastewater using electro-catalytic redox. The embodiments may include (a) adjusting a pH of the nitrotoluene wastewater to 1.5 to 2.0, standing for precipitation, draining sludge of the nitrotoluene wastewater at the bottom, obtaining supernatant of nitrotoluene wastewater, placing the supernatant through a cathode inlet into a cathode chamber of an electrochemical reactor; (b) performing electrochemical treatment, wherein reduction reaction of the supernatant of the nitrotoluene wastewater takes place at the cathode chamber, the nitrotoluene wastewater is placed into the anode chamber for oxidation reaction through the cathode outlet, the catholyte tank, and the anode inlet in sequence; (c) adjusting the nitrotoluene wastewater treated in step (b) via the anolyte tank, and then discharging the nitrotoluene wastewater into a biochemical system. The embodiments reduce toxicity of mixed acid nitration wastewater and therefore improve its biodegradability.