An all-optical cesium magnetometer with high sensitivity based on absorptive detection is reported.The experiment achieves a polarized rotational spectrum of the probe light which is induced by circular dichroism and a quarter wave plate together.The frequency response of the rotational spectrum is 1.8mrad/Hz at Larmor precession resonance.Analyzing the signal-to-noise ratio from the experimentally observed spectrum,we predict that the magnetic measurement sensitivity of 0.3pT/Hz1/2 would be obtained in the responsive range from 20nT to 2000nT.