The invention discloses a device and a method for optimizing the low-speed performance of an internal combustion engine. The internal combustion engine comprises multiple cylinders, an air valve, an air valve actuator and an auxiliary driving mechanism, wherein the air valve actuator generates main valve lift of the internal combustion engine; the main valve life comprises valve lift of an exhaust valve of the internal combustion engine in an exhaust stroke period or valve lift of an air inlet valve of the internal combustion engine in an intake stroke period; the auxiliary driving mechanism generates auxiliary valve lift of the internal combustion engine. When the internal combustion machine is in a low-speed operating state, the method comprises the following steps: (1) generating the auxiliary valve lift in part of the multiple cylinders of the internal combustion engine by use of the auxiliary driving mechanism, wherein the auxiliary valve lift comprises valve lift of the exhaust valve of the internal combustion engine in a compression stroke period or valve lift of the air inlet valve of the internal combustion engine in the compression stroke period; (2) stopping supplying fuels to partial cylinders which generate the auxiliary valve lift; (3) keeping main valve lift of the rest cylinders which do not generate the auxiliary valve lift among the multiple cylinders of the internal combustion engine constant and supplying fuels to the rest cylinders. On the basis, the invention further provides a method and a device for starting the internal combustion engine.