Low fuel regression rate is fatal disadvantage for hybrid rocket. To overcome this problem, a lot of methods have been proposed. In Kyushu university multi-section swirl injection method has been proposed to increase the fuel regression rate and combustion efficiency. This method generates swirling flow in combustion chamber through injector ports located on the some cross-sections over a fuel grain. High density polyethylene and gaseous oxygen were used as propellant. Multi-section swirl injection method shows twice higher fuel regression rate than that of the conventional method with no swirl in the previous study. In the present study, the effects of the number and the diameter of injector ports was investigated under constant total injector ports area condition. To decrease interference of oxidizer flow, the average regression rate increased at low oxidizer mass flux region.