We report a set-up for cavity ringdown absorption spectroscopy, and we have measured the line profile of the resonance 6s6p1P1←6s6s1S0 of barium atoms using cavity ringdown spectroscopy method. The absorption spectroscopy line profile of Ba at different temperatures near 553.548nm is gained. The experimental results indicate that the precision for the absorption measurement has reached up to 6×10-7.