The invention relates to a calibration device for a space electric charge density measuring instrument. The calibration device comprises a photoelectric cathode plate and a shielding/calibrating electrode plate that are arranged opposite to each other at an interval in an insulation cylindrical shell, voltage is provided via an adjustable direct current source, and a uniform electric field is formed; a part, facing right to the shielding/calibrating electrode plate, of the insulation cylindrical shell is provided with a quartz window; ultraviolet light of an ultraviolet light source can enter through the quartz window, the adjustable direct current power can also provide electric power for the photoelectric cathode plate and a collector electrode below the insulation cylindrical shell, a current is detected via a galvanometer, a closed circuit is formed, a top end of the insulation cylindrical shell is provided with a fan, a bottom end is connected with an electric charge density measuring instrument to be calibrated, and the electric charge density measuring instrument to be calibrated is calibrated via comparison between known electric charge density and electric charge density of the electric charge density measuring instrument to be calibrated. The calibration device disclosed in the invention is simple in structure, stable in performance and low in manufacture cost; and the calibration device can be used for calibrating a plurality kinds of space charge density measuring instruments.