Broadband absorption enhancement effect induced by nanocone grating in 1 μm thick Si solar cells has been numerically investigated by rigorous coupled-wave analysis method. Even though the great antireflection performance has been achieved in the nanocone grating of P=100 nm, the higher optical generation rate and ultimate efficiency are achieved in the solar cell with nanocone grating of P=500 nm and H=350 nm, which is 1.4 times and 1.65 times higher than that in planar Si.