In the paper，a measurement method of absolute rotation of atom interferometer is proposed. Generally，there are π/2-π-π/2 phase gratings in an atom interferometer in the space domain. We add three special phases to the three gratings，then，we modulate the special phases to change the detector signal of atom interferometer，and Fourier transform is performed on the detector signal，to obtain the absolute rotation of atom interferometer. The results are the discussed in the paper.