The application of large-diameter rigid monopiles is a growing trend in offshore wind turbine projects. Among the various models used to simulate the lateral response of these monopiles, the {‘p−y’+‘MR−θR’} model has emerged as an effective choice. However, this model has certain limitations, such as its inability to capture the rotation flow mechanism above the pile rotation center and its neglect of vertical friction at soil-pile interface. To address these limitations and enhance our understanding of soil-pile interaction mechanisms for large-diameter rigid monopiles, we develop a modified {‘p−y’+‘MR−θR’+‘ms−θR’} model that accurately captures all three components of soil-pile interaction. This improved model expands the upper range dominated by the concentrated rotation spring to include depths where shear force on the pile section approaches zero, and incorporates distributed moment resistance from vertical shaft friction into consideration. We present several validation cases that demonstrate its superiority over previous methods such as API method and {‘p−y’+‘MR−θR’} method. Additionally, through parametric analysis based on our proposed method, we investigate how pile diameter and eccentricity influence internal mechanisms of soil-pile interaction. Our findings reveal that vertical friction at the soil-pile interface plays a significant role in large-diameter cases while rotation flow mechanism dominates in situations with large-eccentricity. Furthermore, we provide a concise empirical expression for estimating lateral bearing capacity of large-diameter rigid monopiles at serviceability limit state which can be conveniently applied during preliminary design stages in practical engineering.