In order to broaden the absorption range of the active material to the solar spectrum and realized the wide spectrum absorption enhancement of the device.In this paper, a novel organic solar device based on the grating structure is proposed,which introduces gratin gs with different duty ratios in one period to form the cascaded gratings.The effect of cascade g rating structure on the absorption performance of the device is studied by FDTD.The results show th at the broadband absorption enhancement can be realized by exciting multiple surface plasmon reso nances modes and these resonance modes at different wavelengths can exist simultaneously in t he absorption spectrum.Under the TM and TM/TE hybrid polarization mode,the integrated absorp tion efficiency of the active material increased from 23.9% to 54.2% and 36.4%,respectively, compared with that of the equivalent planar structure,and increased by 126.8% a nd 52.3%,respectively.And the wide-angle absorption of the cascaded grating in the range of 0to 65degrees incidence angle can be achieved.The absorption performance of the device is les s sensitive to the slight error of grating parameters and is suitable for the preparation of practi cal nanometer devices.The design and findings of this work can exploit further a pplications of metallic gratings in OSCs devices.