The invention provides a programmable integer/fraction frequency divider, comprising a programmable integer frequency divider and a programmable fraction frequency divider, wherein the divisor of theprogrammable integer frequency divider can be set as at least a first and a second integer according to a divisor switching signal. The programmable fraction frequency divider computes the pulse number of the output signal of the programmable integer frequency divider, when the pulse number of the output signal is equal to an established pulse number, the divisor switching signal is generated to switch the divisor of the programmable integer frequency divider. The established pulse number is determined by the fraction part of the divisor according to the programmable integer/fraction frequencydivider. The fraction frequency divider receives at least one fraction divisor to change the established pulse number, further changing the fraction part.