A structure of one-dimensional Si grating for the Si solar cells is proposed. The solar energy absorption characteristics of this structure are studied by the finite difference time domain (FDTD) method. By alternately altering the grating depth, a new type of grating structure is proposed. For such a structure, three different gratings with depth of 50 nm, 100 nm and 150 nm in every grating period are studied. The effects of incident angle and temperature on the absorptance and efficiencies are discussed. Numerical computation shows that the absorptance of the assembly Si grating structure is over 0.85 throughout the entire computational band. The conversion efficiency of solar cells with such grating surface amounts to as high as 27.97%, which indicates the proposed structured surface may have potential applications in solar-cells manufacturing. (C) 2011 Elsevier Ltd. All rights reserved.