<p>Rolling turbine, also known as a precession turbine, is a low-head water turbine designed to generate electricity from small rivers and streams. It is environmentally friendly and can be deployed in ecologically sensitive areas. In this paper, 3D CFD simulation combined with second-order polynomial-based response surface method (RSM) was applied in order to enhance the output torque of the turbine. To capture the rotation of the rotor, the immersed solid method was employed. Different shapes of rollers including sphere, hemisphere, and truncated cone were studied and compared using numerical simulations. The results showed that the truncated cone has the better performance than the other rollers. A preliminary study was conducted for truncated cone roller to specify design variables. Diameter ratios (<i>D</i>₁/<i>D</i>, and <i>D</i>₂/<i>D</i>) were employed as design variables. The torque on the precision shaft was applied as the objective function. The objective function was transformed to dimensionless form (<i>T</i>/<i>T</i>_ref). The optimum value was predicted to be <i>T</i>/<i>T</i>_ref = 1.284, which showed an increment of 0.284. The optimal values of design variables were <i>D</i>₁/<i>D</i> = 0.926, and <i>D</i>₂/<i>D</i> = 0.187. Analysis of variance showed that <i>D</i>₁/<i>D</i>, <i>D</i>₂/<i>D</i>, <i>D</i>₁/<i>D</i>*<i>D</i>₂/<i>D</i>, and (<i>D</i>₂/<i>D</i>)² are significant model terms.</p>