The finite element model of sheet-shaped phononic crystals was established with Patran software, and the results of simulation showed that the band gap was between 164 and 353 Hz. A simplified model of Z-mode of bending vibration for sheet-shaped phononic crystals was proposed. The effect of material parameters, such as the density of scatter, the thickness of coating, and the constraint condition on the band gap was analyzed. The phononic crystal samples made of acrylic, steel, and silicone were provided, and their transmission characteristics were tested experimentally. The result shows that there are obvious band gaps below 2 000 Hz, and the attenuation of vibration amplitude can exceed 40 dB. This work may provide a reference for application of phononic crystals to vibration attenuation of sheet-shaped component parts of automotives.