The present invention provides a field emission system and a method for improving its vacuum. The present invention employs aging surface-unsaturated carbon nanotubes in non-display areas of the field emission system as getter material to absorb residual gas within the system so as to improve its vacuum. The present method for improving vacuum of the field emission system can be integrated with the standard process of a field emission display device without additional fabricating steps, and thus facilitating the mass production of the field emission display device.