This work investigates the corona inception voltage and the motion of space charge near a rod-plane electrode under combined DC-AC voltages. For a high AC component, the corona inception voltage of the equivalent negative corona exceeds that of the equivalent positive corona. For a small AC component, the corona inception voltage of the equivalent positive corona exceeds that of the equivalent negative corona. The corona inception voltage decreases with increasing AC component. The charge-motion model based on hydrodynamics is used to analyze the charge motion for different AC/DC voltage ratios. The charge remaining for equivalent negative coronas exceeds that for equivalent positive coronas with high AC components. In addition, the charge remaining for equivalent positive coronas exceeds that of equivalent negative coronas with small AC components. As the AC component decreases, the remaining space charge increases. The results show that space charge tends to “block” corona inception. The more space charge remains, the higher the corona inception voltage is. Therefore, the variation in space charge and the corona inception threshold conditions under combined DC-AC voltage differ from those under only DC or AC voltage.