Recently, hybrid rockets have attracted a lot of interests, because it has main some advantages of low cost, safety, and thrust throttling. On the other hand, launching practical satellites, hybrid rocket has technical problems to overcome, such as low fuel regression rate and low combustion effic iency. In order to improve fuel regression rate and combustion efficiency, a new method with multi-section swirl injection was proposed. In the previous study, it was proved that this method was very effective in increasing fuel regression rate, combustion efficiency, and thrust of hybrid rocket engines. Especially, the fuel regression rate for paraffin fuels with multi-section swirl injection method reaches to about 3 to 10 times higher than that of the no-swirl conventional method. Additionally, deep grooves like erosion are observed on the surface around injector ports of fuel grains after combustion tests. In this paper, combustion tests for several grain types were conducted to clarify influences of difference in the number and diameter of injector ports on the regression rate.