The invention discloses a Miller cycle diesel oil-natural gas dual fuel engine and a control method thereof, and relates to the technical field of engines. An early closing mode of an intake valve is realized through adjusting an intake valve adjusting mechanism; and a compression ratio is changed to separate from an expansion ratio, so that the cooling of mixed gas is facilitated, the thermal load of the engine is reduced, the positive suction power is generated in the expansion process to improve the thermal efficiency of the engine, and the fuel economy is preferably improved. The new control method is used for converting high/low compression ratio more flexibly, so that the diesel oil-natural gas dual fuel engine can achieve high-efficiency combustion operation in a full-load range.