Abstract: In order to achieve broadband and efficient absorption of low-frequency sound waves in open ducts, a systematic design of nested slit-type resonator-based acoustic metamaterials is proposed in this paper. By using the transfer matrix method, the effective acoustic impedance and acoustic transmission response of the nested slit-type resonator unit are theoretically derived and analyzed, which reveals that such a design can increase the density of the resonance absorption states of the unit and shift the first absorption peak to lower frequencies without changing the overall size of the structure. The numerical simulation results verify the accuracy of the scheme. Based on this, units with different weak resonance absorption peaks are spatially combined with their specific structural parameters being globally optimized through the genetic algorithm, which enables low-frequency, broadband and efficient sound energy absorption based on the weak resonance coherent coupling effect between units. The experimental results show that the average sound absorption effect of the sound-absorbing metamaterial composed of 15 nested slit-type resonators can reach more than 87% in the wide frequency range of 500−2000 Hz.