The invention discloses a plasma processing device which comprises a reaction chamber and a cooler. The reaction chamber comprises an electrostatic chuck which is used for clamping a substrate to be processor and is internally provided with a cooling path. The cooling path is provided with an inlet end and an outlet end. The output end and the input end of the cooler are respectively connected with the inlet end and the outlet end of the cooling path through transmission pipelines, and are used for circularly supplying coolant to the cooling path. A first temperature sensor is arranged at the inlet end of the cooling path, and a second temperature sensor is arranged at the outlet end of the cooling path. The cooler comprises a temperature control unit and an actuating unit. The temperature control unit adjusts the power of the actuating unit according to a difference between coolant temperatures at the inlet end and the outlet end of the cooling path and the difference between the coolant temperature at the outlet end and the target temperature of the electrostatic chuck, thereby making the coolant temperature at the outlet end of the cooling path reach the target temperature. The invention further provides a corresponding temperature control method. The plasma processing device and the temperature control method thereof can improve accuracy and timeliness in substrate temperature controlling.