The swept light source is a key component of the swept source optic coherence tomography (SSOCT).A high quality swept light source can improve the imaging speed, resolution and signal-to-noise ratio of the SSOCT. In this work, a ring-cavity swept source was built by using fiber acousto-optical tunable filter (FAOTF), polarization-maintaining booster optical amplifier (PMBOA), fiber isolator and fiber coupler. The experimental results show that an all-fiber swept light source with the sweep speed of 100 kHz, sweep range of 119 nm (from 1 550.146 2 nm to 1 619.470 0 nm), single spectrum 3 dB bandwidth of 0.096 6 nm and average optical output power of 12 mW has been realized. The swept source has the advantages of wide sweep frequency range, fast speed, and good coherence and so on. It has certain practical value as a light source in SSOCT system.