Satellite calibration antenna suffered rigorous vibration environment in the course of lunching. Random vibration is being specified for acceptance tests by spacecraft structure. The waveguide tube of antenna was cracked in the random vibration test. Fracture analysis using scanning electron microscopic showed that failure were induced by fatigue damage. Finite element model of antenna was built and root mean square (rms) stress of waveguide tube was obtained in random vibration analysis. The maximum rms stress was 35.6MPa and located at the flange base. Then fatigue life of waveguide tube was estimated, using the Palgren-Miner rule and the three-band method. The estimated fatigue life of 109 seconds showed the waveguide tube couldn’t ensure safety during 120 seconds of the random vibration. Finally two ribs were added at each flange base for decreasing the stress concentration. The fatigue life of improved waveguide tube was 811 seconds. Then it passed the random vibration test.