Taking the roller—floating bush—roller pin in the fuel supply mechanism of Marine diesel engines as the research object, considering its elastic deformation and surface roughness characteristics under low-speed and heavy-load working conditions, a thermoelastic hydrodynamic lubrication analysis model of the double-layer oil film inside and outside the float bushing was established. The influence laws of the gap ratio of the inner and outer oil films, the width-to-diameter ratio of the bushing, the thickness of the bushing and its surface roughness on the lubrication characteristics such as the ring speed ratio, the maximum oil film pressure of the inner and outer layers and the bearing capacity were discussed. The results show that during the operation of the roller-float bushing—roller-pin structure, the thickness of the internal oil film is relatively small and the lubrication state is poor. Under low-speed and heavy-load working conditions, the elastic deformation of the bushing and the mixed lubrication effect cannot be ignored. The larger the width-to-diameter ratio and the smaller the gap ratio between the inner and outer layers, the smaller the maximum oil film pressure, the stronger the structural bearing capacity, but the higher the temperature rise. The mixed lubrication state only occurs within the inner lubricating oil film of the bushing. The greater the surface roughness of the bushing, the worse the lubrication effect.