A method for generating a spread spectrum clock includes the steps of providing a reference clock having a reference period; generating a plurality of output clocks respectively having different phases according to the reference clock; generating a first/second control signal according to the reference clock and a spread spectrum clock and starting a first/second duration accordingly; during the first/second duration, outputting a first/second selecting signal representing a first/second predetermined sequence according to the first/second control signal, wherein the second predetermined sequence is a substantial reversed sequence of the first predetermined sequence; and during the first/second duration, sequentially outputting some or all of the output clocks as the spread spectrum clock according to the first/second predetermined sequence.