System and method for controlling spark-ignition internal combustion engine

A control system controls a spark-ignition internal combustion engine (11). The spark-ignition internal combustion engine (11) includes a cylinder (12), and a fuel injection valve (17) arranged in the cylinder (12); and an intake port (20) that communicates with the cylinder (12), and a fuel injection valve (22) arranged in the intake port (20). Fuel is injected from both the fuel injection valves in at least a part of an operating range. If combustion fluctuations exceed a predetermined amount, in consideration of a preset proportion of fuels to be injected into the cylinder (12) and the intake port (20), a proportion of fuel to be injected into the cylinder (12) is decreased and a proportion of fuel to be injected into the intake port (20) is increased.