The invention relates to a combination drug composition for treating liver cancer. The combination drug composition is prepared from a PARP1 protein inhibitor Olaparib and a DNA-PKcs protein inhibitorNU7441. A DNA double strand breakage repair passage in a liver cancer cell is highly activated by protein inhibited by the combination drug composition, and accordingly an effective target spot is provided for treating liver cancer. Compared with the prior art, the micromolecular drug Olaparib can interdict homologous recombination repairing and selective non-homologous end joining repairing in liver cancer tissue, while NU7441 can interdict the non-homologous end jointing repairing, so that a combination of the two drugs can completely interdict the DNA double strand breakage repairing passage and thereby effectively inhibit proliferation of liver cancer, and the tumor increasing inhibition rate is as lowest as 62.3%, and as highest as 83.9%.