A method of designing X-band low phase noise frequency synthesizer is proposed. By combining the mixer-Phase Locked Loop(PLL) and the analog of high order multiplier, the hopping signal of X-band is realized. The synthesizer can achieve specifications including spurious-suppress below -68 dBc and phase noise below -99 dBc/Hz@1 kHz, -104 dBc/Hz@10 kHz, -106 dBc/Hz@100 kHz. It emphasizes the key techniques of low phase noise multiplier using step recovery diode, and analyzes the method of implementing specifications. Through the measured results, it is demonstrated that the method can design the X-band low phase noise frequency synthesizer achieving the given specifications.