The invention discloses a tool changing device and method for a numerical control machine tool. The device comprises a tool magazine mechanism, a main shaft box, a main shaft and a tool changing mechanism. The main shaft box is provided with a main shaft tool loosening mechanism used for releasing a tool at the lower end of the main shaft, the main shaft tool loosening mechanism comprises a tool loosening base and a tool loosening arm, the tool loosening base is fixedly installed on the main shaft box, the tool loosening arm is provided with a tool loosening roller used for pressing a pressingrod on the main shaft, the main shaft tool loosening mechanism further comprises a servo driving device, the servo driving device is arranged on the tool loosening base, the driving end of the servodriving device is vertically downward, one end of the tool loosening arm is rotationally connected to the main shaft box, the other end of the tool loosening arm is located under the driving end of the servo driving device, a connecting rod mechanism is arranged between the middle of the tool loosening arm and the tool loosening base, and the connecting rod mechanism is used for enabling the end,located below the servo driving device, of the tool loosening arm to be in a suspended mode. According to the key point of the technical scheme, the tool changing device of the numerical control machine tool improves tool changing efficiency in the way of loosening the tool in advance.