Acoustic barriers with Helmholtz resonant structures have potential in controlling traffic road noise. In order to effectively improve the noise control in a specific frequency band, a Helmholtz composite resonator structure with four secondary resonators is designed in this paper. Firstly, the finite element method is used to calculate and analyze the resonator model, and the band gap structure and sound transmission loss curve of the resonator are obtained. Secondly, the equivalent circuit of Helmholtz resonator is established by acoustic-electric analogy method, and the generation mechanism of band gap is analyzed. Finally, the influence of structural parameters on the band gap of Helmholtz resonator is discussed, and the mechanism of these parameters on the lower limit of the first band gap is analyzed. The results show that the sound wave has interaction and cavity resonance effect among the Helmholtz cavity elements at the same time. The first band gap in the range of 432.43 Hz to 663.98 Hz can be obtained when the lattice constant is 60 mm, which is lower than the initial frequency of the band gap of the opening ring. The sound insulation in most frequency ranges reaches more than 10 dB, and the maximum sound insulation exceeds 90 dB, which shows better intermediate frequency sound insulation characteristics. The maximum error between the equivalent circuit model and the calculated value of the finite element method does not exceed 10% and the average error is less than 5%, the established equivalent model is reasonable. The structure parameters have a great influence on the band gap by affecting the volume of gas in the cavity.