In order to explore the tolerance of Acorus calamus on Orange G dyeing wastewater and the feasibility of its remediation of dyeing wastewater pollution, we determined photosynthesis, chlorophyll fluorescence parameters and antioxidant enzymes activity of Acorus calamus in nine dye concentrations (0, 60, 120, 180, 240, 300, 360, 420 and 480 mg·L^–1) using hydroponics. Orange G inhibited the photosynthesis of Acorus calamus, which presented as decreased net photosynthesis rate (P_n), maximum quantum yield of PSII (F_v/F_m) and actual photochemical efficiency (Φ_PSⅡ). P_n and stomatal conduction (G_s) decreased and intercellular CO₂ concentration (C_i) increased with increasing concentration of Orange G, showing that the main reason for restricting P_n had turn into non-stomatal limitation; The activities of the antioxidant enzyme were activated in the dye concentration below 120 mg·L^-1, and the antioxidant enzyme system was damaged in the dye concentration above 120 mg·L^-1. These results implied that function of photosynthetic apparatus in Acorus calamus seedling leaves was maintained by a synergistic effect of thermal energy dissipation and regulating the antioxidant enzymatic activity jointly. Non-stomatal limitation responsible for reduction in P_n was associated with the impairment of PSⅡ and antioxidant enzyme system when dye concentration was above 120 mg·L^-1.