Previous research on water erosion has primarily focused on arid and semi-arid regions, with less attention given to tropical areas. The rapid expansion of rubber cultivation in tropical areas has significantly altered the vegetation structure, making the spatial-temporal evolution of soil erosion and its impact mechanisms unclear. Traditional evaluation methods often overlook how varying rainfall intensities impact vegetation across different periods. Therefore, this research applied the Chinese soil loss equation model, the optimal parameter geographical detector model, and the logarithmic mean divisia index model to calculate the soil erosion modulus of Hainan Island and determine the influence of various factors on soil water erosion. The soil erosion modulus in 68.89% of the regions exhibited an increasing trend, indicating a risk of soil erosion. Slope, elevation and the NDVI play key roles in determining the spatial variation of water erosion on Hainan Island. The shift from tropical rainforests to rubber plantations diminishes the soil conservation capacity of the understory vegetation, thereby exacerbating soil erosion. This study lays the groundwork for an understanding of soil erosion mechanisms associated with rubber forest expansion and soil protection and ecological conservation in Hainan Island, and offers valuable insights for future research in similar regions.