The present invention provides a method for controlling a compression ignition internal combustion engine, which can easily cope with a wide range of demand loads. The compression ignition internal combustion engine 1 has a first fuel 2 containing ethanol, and reforming means 5 for reforming the first fuel into a second fuel having higher ignitability than the first fuel, by converting at least one part of ethanol contained in the first fuel 2 to diethyl ether, and each amount of the first fuel and the second fuel to be supplied to the compression ignition internal combustion engine is varied, in accordance with the change of a load required to the compression ignition internal combustion engine 1. Thus, the proportion of the first fuel to the total fuels supplied to the internal combustion engine 1 is increased, with the increase of the demand load, while the proportion of the second fuel to the total fuels supplied to the internal combustion engine 1 is increased, with the decrease of the demand load. The first fuel 2 contains ethanol and a hydrocarbon which is liquid at room temperature.