A new high-efficiency light-trapping structure (HE-LTS) with two cavities is proposed and designed for ultrathin c-Si solar cells. The results show that by optimizing the size parameters of the HE-LTS, the photocurrent density value of a c-Si solar cell with its active layer equal to 4.5 μm is close to that of Lambertian LTS at each wavelength in the range from 300 nm to 970 nm and greatly exceeds that of Lambertian LTS at each wavelength in the range from 970 nm to 1200 nm; the photocurrent density of the HE-LTS can exceed that of Lambertian LTS by adjusting the size parameters in a wide range.