Abstract: To study the evolution of planet and space environment, the space plasma is always detected in space scientific mission. The standard ion source is crucial for calibrating the space applied ions detector. A low energy ion source based on carbon nanotube emitter has been constructed and investigated. The ion source could be used in calibration of low energy ion detection instruments on the ground. As the results shown, 1 μA could be extracted and used in ionizing gas molecular while the emission current was stabilized around 70 μA. In the experiment, 10 pA argon ions current corresponding ion density of 200 cm^-3 was produced and kept stable for 95 minutes with sensitivity fluctuation of lower than 19%.