The invention aims at providing a combined mechanical fuel oil injection and electromagnetic fuel gas injection mixed fuel injection device. The mixed fuel injection device comprises a control part, a dual-needle-valve nozzle part, an injection device upper end cover and an injection device shell. A dual-needle-valve nozzle is adopted to inject fuel oil and fuel gas, the space is saved, and the engine structure is simplified; a mechanical structure is adopted to control the fuel oil injection process, the structure is simple, and succession to an existing diesel engine is good. A fuel oil leakage channel is controlled to flow through the upper portion of an electromagnetic valve body, the effect of cooling an electromagnetic valve is achieved, and the working stability of the electromagnetic valve is improved; a sealing annular band is arranged on the portion, above a gas chamber, between a fuel gas needle valve and a needle valve base, partial control oil is introduced to the sealing annular band to seal fuel gas, and fuel gas leakage can be effectively prevented; meanwhile, control oil in a control cavity and sealing oil at the sealing annular band adopt the same oil, and it can be effectively guaranteed that the control oil and the sealing oil are free of static leakage.