In this paper a new phase contrast method with fringe contrast adjustable is proposed. In the Fourier plane of the object wave, two Ronchi gratings i.e., a central grating and a surrounding grating, are used to modulate the phases of the undiffracted and diffracted components, respectively. By loading the two gratings separately on spatial light modulator, the undiffracted and diffracted components can be measured independently, which simplify greatly the reconstruction process. Besides, the fringe contrast of the phase contrast interferogram can be adjusted by changing the modulation depth of the two gratings. The feasibility of the proposed method is verified by theoretical analysis and experiment.