The invention provides an ultra-wide band circularly polarized reader-writer antenna comprising a dielectric plate and a metal antenna sheet attached to the surface of the dielectric plate. The metal antenna sheet comprises an earth tag, a first radiating unit and a second radiating unit; the first radiating unit and the second radiating unit are connected with the earth tag; the first radiating unit comprises a first branch with one end connected with the earth tag and a second branch with one end connected with the first branch; the second radiating unit comprises a third branch with one end connected with the earth tag and a fourth branch with one end perpendicularly connected with the third branch; the first branch and the second branch are different in length and resonance frequency point. The ultra-wide band circularly polarized reader-writer antenna has excellent matching characteristics at the overall ultra-high frequency band, also has the circular polarization characteristic and has the advantages of small dimension, simple structure, low manufacturing cost and the like.