The invention provides a method for in situ compounding preparation of a graphene-based lithium-rich layered lithium manganate electrode material, wherein graphite is adopted as a raw material, a lithium ion solution and a manganese ion solution are penetrated into the graphite interlayer to form intercalating graphite, the graphite is subjected to mechanical stripping to obtain a lithium ion and manganese ion uniformly-compounding graphene slurry, a reducing agent is added in a hydrothermal environment, a nano-scale lithium manganate material is formed in an in-situ manner, and calcining is performed to obtain the graphene-based lithium-rich layered lithium manganate electrode material. According to the present invention, with the method, the disadvantages of high energy consumption, long time, poor electric conductivity and non-uniform particle size after the compounding with graphite due to easy agglomeration in the prior art are overcome, the in situ compounding of the graphene-based lithium-rich layered lithium manganate electrode material and graphene is achieved, and the high-temperature stability of the lithium manganate crystal structure is improved so as to further improve the battery cycle life.