A new kind of optical absorber based on surface plasmonic gratings with depth-linear-gradient grooves is designed. The effects of structural parameters and the light incident angle on the absorption characteristics within the visible wavelength range are analyzed by the finite element method. The proposed optical absorber is also compared with other optical absorbers with symmetrical groove depths. Results indicate that, increasing the number of grooves, groove width, and groove depth of air grooves, as well as reducing the center distance of adjacent air grooves, all can effectively enhanced the light absorption efficiency. The absorption performance of optical absorber here is superior to that of other optical absorber with symmetrical groove depth.