A projection system, a protection circuit and a current monitoring method of an image resolution enhancement device are provided. A light valve converts an illumination beam into an image beam. The image resolution enhancement device changes a transmission path of the image beam according to a driving current. The protection circuit detects the driving current. When the driving current is greater than or equal to a first current threshold, the protection circuit further compares the driving current with a second current threshold. When a duration time that the driving current is smaller than the second current threshold and greater than or equal to the first current threshold is greater than or equal to a time threshold, the protection circuit decreases the driving current to be smaller than the first current threshold to control the image resolution enhancement device. The projection lens converts the image beam into a projection beam.