Sound barriers have been widely used in road traffic noise pollution prevention, however, they face problems such as limited sound absorption performance and lightweight grade of materials. In order to better improve the noise reduction effect of road sound barriers, it is necessary to study the acoustic performance of composite acoustic structures and their influencing factors. A two-dimensional finite element model of an impedance tube was established, and its reliability was verified by comparing it with experimental data. Based on the finite element simulation, a micro-perforated plate - double-layer porous acoustic material - cavity composite acoustic structure was constructed, and the influence of geometric parameters on the acoustic performance of the composite structure was studied and simulated in the road scenario. The results show that the aperture diameter and plate thickness of the micro-perforated plate decrease, the sound absorption effect of the composite structure in the medium-high frequency band is improved; the perforation rate decreases, the sound absorption performance of the composite structure in the low-frequency band is improved, but that in the medium-high frequency is significantly reduced; the increase in the thickness of the porous material improves the sound absorption coefficient in the medium-high frequency of the composite structure. The reasonable placement of cavities behind the porous material does not reduce the acoustic performance of the composite structure. The composite structure consists of a micro-perforated plate with a 3% perforation rate, 0.4 mm aperture diameter, and 1 mm plate thickness and 3 cm polyester fiber + 3 cm melamine + 2 cm cavity has a better noise reduction effect, and it was used as the material of the sound-absorbing acoustic barrier. The laws of insertion loss of sound-absorbing and sound-insulating sound barriers are basically the same. The insertion loss of the sound-absorbing sound barrier with composite structure was improved by 1-2 dB compared with that of the sound-insulating sound barrier. Therefore, the designed composite structure can effectively control traffic noise mainly at low and medium frequencies, which has practical engineering value.