To address the high cost of foundations for offshore wind turbines in deep and far-sea environments, a novel gravel-filled canister-monopile (GCM) was proposed, which consists of three components: a large-diameter monopile, a steel canister, and gravel filled between the pile and the canister. During service, the gravel was able to fill gaps generated in the pile–soil interface due to long-term cyclic loading, effectively mitigating the weakening of the surrounding soil and thereby enhancing the lateral bearing capacity of the monopile. To analyze the lateral bearing behavior of the gravel-filled canister-monopile, a strain wedge coupled model considering pile–canister deformation coordination was developed, taking into account the increase in lateral support stiffness provided by the filled gravel and the horizontal displacement development of the canister under load. By reducing the canister diameter to that of the pile, setting the canister height to zero, and treating the filled gravel as surrounding soil, the proposed model degenerated into a conventional monopile lateral bearing model, which was validated through comparison with existing analytical theories. Further comparisons with finite element analysis results confirmed the reasonableness and reliability of the proposed model. Based on the validated model, a parametric analysis of the main design parameters of the gravel-filled canister-monopile was conducted. The results indicated that the steel canister diameter, height, and the elastic modulus of the gravel were all positively correlated with the lateral bearing capacity, while the canister embedment depth exhibited an optimal design value.