Oil spills and industrial and household oily wastewater discharge cause environmental and economic concerns. Emerging Janus membranes have generated widespread interest as next-generation oil/water separation membranes with anisotropic wettability because of their specific, on-demand separation ability. However, the one-step separation of complex wastewater remains to be achieved. Herein, a pH-responsive modified polystyrene microspheres/zinc oxide/carbon nanotubes/polyvinylidene fluoride (S/PS/ZnO/CNTs/PVDF) membrane is rationally designed with Janus surfaces for hydrophilicity/underwater lipophobicity and lipophilicity/underoil hydrophobicity. This study demonstrates that the underlying mechanism of on-demand water-in-oil and oil-in-water emulsion separation is related to wettability, adhesive force, and intrusion pressure. The Janus membrane can achieve one-step separation of complex wastewater comprising oil, bacteria, organic dye, and metal ions. The effective removal of dyes is due to synergistic effects of electrostatic adsorption and photodegradation. This facile strategy for construction of a smart Janus separation membrane has application potential in on-demand oil/water separation and practical complex wastewater separation.