The phase noise measurement system based on fiber delay line has been realized in this paper,including complete theoretical model and its control servo,and the correctness of the measurement data has also been verified by experiments.In order to improve the sensitivity of the measurement system,the noise figure of microw ave photonic link is optimized to reduce the noise floor near carrier′s frequency.Photo-diode with high linearity and low phase noise amplifier is also used to reduce the parasitic effect of 1/f noise,resulting in low noise floor remote carrier′s frequency.High-sensitivity phase noise measurement system is realized and its noise floor at X band is －130dBc/Hz a t 1kHz and －145dBc/Hz at 10kHz.