In order to know the AC corona initiation voltage changing of rod-plate electrodes under different humidity and electrical conductivity, an artificial climate box is used to perform corona discharge experiments on iron rod electrodes with a radius of 3mm under different humidity and different electrical conductivity conditions. Using general tap water and ultrasonic humidifier to achieve different humidity, the photon numbers of the rod electrode are recorded with the different voltage. By adding salt into the tap water in the ultrasonic humidifier, the different electrical conductivity circumstance of the rod-plate electrodes are achieved. Under humidity of 96.6%, the photon numbers of the rod electrode are recorded with the different electrical conductivity and voltage. The tangent method is utilized to get the corona initiation voltage. The results show that when the humidity is in the range of 50%-85% at the same electrical conductivity, the corona initiation voltage decreases with the increase of the humidity, and at the humidity of 96.6%, the corona initiation voltage of the rod-plate electrode decreases with the increases of the electrical conductivity of the salted tap water. When the electrical conductivity of the salted tap water is 4760μS/cm, its corona initiation voltage drops by 34.9% compared to the corona initiation voltage of general tap water with electrical conductivity 210μS/cm.