The quadratic Zeeman coefficient was previously measured by using the single pulse spectroscopy method, in which the experimental resolution is limited by the line width of the spectrum of the clock transition. In this paper, an accurate measurement of the quadratic Zeeman coefficient is presented by using the Ramsey atom interferometer. The line width of the central Ramsey fringe of the 87 Rb clock transition, which depends on the interrogation time, is much narrower than that of the single pulse spectroscopy method. The measurement uncertainty of less than 1 Hz G −2 is realized, which is much better than the other current existing results. The measured quadratic Zeeman coefficient of the 87 Rb clock transition is 575.33±0.36 Hz G −2 by the Raman Ramsey atom interferometer, and 575.48 ± 0.30 Hz G −2 by the microwave Ramsey atom interferometer, which coincides well with the theoretical result of 575.15 Hz G −2 calculated by the Breit-Rabi formula.