The narrow annulus in slimhole horizontal wells leads to significant differences in Cuttings transport，compared to conventional horizontal wells. To investigate the cutting transport mechanisms in slimhole horizontal wells，a CFD-based numerical model accounting for drill string eccentricity was developed for solid-liquid two-phase flow in the annulus. This study analyzed the effects of key factors，including flow rates，drill pipe rotation speeds，well inclination angles，and drilling fluid properties，on cutting transport in slimhole horizontal wells. The results showed that increasing the drill pipe rotation speed enhances the tangential and axial velocities of the annular fluid and expands the "viscous coupling" region. This facilitates the upward movement of cuttings from the lower side to the upper side of the annulus，thereby improving transport efficiency. Critical thresholds for "rotation speeds" and "flow rates" were identified in highly inclined sections，where cutting transport becomes the most challenging with the two parameters both below the thresholds，and in horizontal sections，where transport becomes more difficult with the two parameters both exceeding the thresholds. Increasing the drilling fluid density enhances the buoyancy acting on cuttings and reduces deposition. The effects of drilling fluid rheological parameters on wellbore cleanup exhibit non-linear trends，with an optimal range existing under different flow rates and rotation speeds. The findings of this research provide theoretical support for optimizing hydraulic parameters in slimhole horizontal wells and preventing issues like drill string sticking.