A clock self-testing method and circuit. The clock self-testing method includes introducing a first clock signal and a second clock signal, counting cycles of the first clock signal and the second clock signal respectively beginning at the same moment, and if one of the number of cycles of the first clock signal being counted and the number of cycles of the second clock signal being counted is equal to N, determining whether the remained number of cycles is in a count range from M to N. If the remained number of cycles is out of the count range from M to N, the first clock signal and the second clock signal have errors.