A method for operating a display device, the method comprising: receiving, by a voice recognition unit of the display device, a voice command of a user; determining, by the voice recognition unit, whether text data corresponding to the received voice command matches with a prestored text pattern in a speech to text database; if a text data corresponding to the voice command does not match with the prestored text pattern, transmitting, by the voice recognition unit, the voice command to a speech to text server which converts the voice command into text pattern; receiving (Sill), by a natural language recognition processing unit of the display device, the converted text pattern corresponding to the voice command from the speech to text server; checking whether the converted text pattern matches with a prestored voice recognition pattern in a natural language processing database storing a corresponding relationship between functions of the display device and voice recognition patterns so as to perform a function of the display device corresponding to the converted text pattern; if the converted text pattern does not match with the prestored voice recognition pattern and exceeds a reference user frequency, transmitting the converted text pattern to a natural language recognition processing server which analyzes an intention of the converted text pattern; receiving the analyzed intention of the converted text pattern; matching by a natural language recognition processing unit, the converted text pattern corresponding to the voice command with the function of the display device on the basis of the intention analysis result and storing the matched result in the natural language processing database; and if the voice command is again received, performing, by a control unit of the display device, the function of the display device corresponding to the again received voice command. receiving, by a voice recognition unit of the display device, a voice command of a user; determining, by the voice recognition unit, whether text data corresponding to the received voice command matches with a prestored text pattern in a speech to text database; if a text data corresponding to the voice command does not match with the prestored text pattern, transmitting, by the voice recognition unit, the voice command to a speech to text server which converts the voice command into text pattern; receiving (Sill), by a natural language recognition processing unit of the display device, the converted text pattern corresponding to the voice command from the speech to text server; checking whether the converted text pattern matches with a prestored voice recognition pattern in a natural language processing database storing a corresponding relationship between functions of the display device and voice recognition patterns so as to perform a function of the display device corresponding to the converted text pattern; if the converted text pattern does not match with the prestored voice recognition pattern and exceeds a reference user frequency, transmitting the converted text pattern to a natural language recognition processing server which analyzes an intention of the converted text pattern; receiving the analyzed intention of the converted text pattern; matching by a natural language recognition processing unit, the converted text pattern corresponding to the voice command with the function of the display device on the basis of the intention analysis result and storing the matched result in the natural language processing database; and if the voice command is again received, performing, by a control unit of the display device, the function of the display device corresponding to the again received voice command.