A multi-phase clock generator including a first delay locked loop, a reference signal generator and a second delay locked loop is provided. The first delay locked loop generates 2N phase clock signals according to an input clock signal, so as to equally divide a clock period of the input clock signal into 2N predetermined phases, where N is a positive integer. The reference signal generator selects two phase clock signals according to a digital signal, and adjusts an output ratio of the two phase clock signals in 2M clock periods to serve as a reference clock signal. The second delay locked loop delays a first phase clock signal according to a phase difference between the reference clock signal and an output clock signal. In this way, each predetermined phase is further equally divided into 2M sub-phases, so that the multi-phase clock generator has 2(N+M) phase selections.