A projection system is provided. The projection system includes at least one micro LED line and a scan optical system. The micro LED line is configured for emitting lights with a changing frequency of X times per second. The scan optical system is disposed at a downstream side of the at least one micro LED line. The scan optical system is configured to scan the lights emitted from the micro LED line with a scan rate of M seconds per scan and to project images formed of the lights to corresponding positions on a target projection plane. The projection system has a horizontal resolution of N lines. A total number n of the at least one micro LED line is smaller than N. Also, X=M*(N/n).