By implying the density functional theory method, the geometry of acetophenone molecular is fully optimized at the B3LYP/6-311++G(d,p) level and the frequency is also calculated at the same level. The infrared spectrum and complete vibrational modes of acetophenone molecular are attained. Meanwhile, the infrared spectrum is obtained by experimental measurements. Through the comparison and analysis, it is found that the theoretical calculation results meet well with those of experiments. Finally, the vibrational modes of acetophenone molecule are assigned, and the strong vibration peaks in the experiment results belong to infrared characteristic peaks of acetophenone molecule.