The invention provides an energy management method for an electric automobile in a range extending mode. The method is put forward and achieved on the basis of the Pontryagin minimum principle in the optimal control theory, the lowest whole automobile fuel consumption serves as an optimization target, a Hamiltonian function of a system is established, and the value of the function is minimal, so that the optimal power distribution between a range extender and a power battery is guaranteed. A control factor, namely an association state variable lambda in the Hamiltonian function is updated online, and the adaptability of electric quantity maintenance control to the travel working condition is achieved. By the adoption of the engineering-feasible energy management method for the range-extending type electric automobile, the technical problems that a hybrid power system is low in energy efficiency, and electric quantity maintenance control of a power battery cannot well adapt to the changes of the travel working condition when an existing range-extending type electric automobile works in the range extending mode can be solved.