The invention discloses a processing device for cationic dye wastewater and a wastewater processing method of the processing device. The processing device comprises a primary filter grid, an electrolytic cell, a sedimentation tank and active carbon columns, wherein the primary filter grid is arranged at the water inlet of the electrolytic cell; the electrolytic cell is connected with the sedimentation tank; the water outlet of the electrolytic cell is the water inlet of the sedimentation tank; the water outlets of the sedimentation tank are connected with the active carbon columns. The processing method comprises the following steps: filtering the cationic dye wastewater by the primary filter grid for entering into the electrolytic cell, and regulating the pH to be 4.0; exerting voltage on a negative electrode and a positive electrode of the electrolytic cell for generating iron ions; introducing the reacted wastewater into the sedimentation tank, regulating the pH to be 8.0-9.0, and enabling the wastewater to enter into a water distribution area after sediment; introducing the active carbon columns for filtering decolorization, and discharging or recycling the wastewater when the wastewater reaches the standard. After the cationic dye wastewater is processed by the processing device and the processing method, the BOD removal rate can reach above 87%, and the removal rates of COD, chromaticness, SS and total copper can reach above 90%.