A kind of locally resonant phononic crystal plate with composite unite was introduced, and the band gap characteristics and sound transmission loss of the proposed structure were investigated with the finite element methods. It is found that the interaction between the local resonances and the traveling wave modes in the plate results the locally resonant band gap, whose bandwidth and sound insulation effect depend on the interaction strength and the thickness of thin membrane by changing structure parameters. By changing the thickness of the thin membrane, the proposed phononic crystal structure is demonstrated to meet the normal flight. The results show that the structures possess sound insulation effect below 200 dB and highest sound transmission loss up to 150 dB. The study provides a theoretical basis to obtain good sound insulation effect, and has a potential application value in the reducing of noise and vibration in the aero-engine.