The invention relates to the technical field of lithium ion batteries, in particular to core-shell structured carbon for a cathode material of a lithium ion battery and a preparation method thereof, and the lithium ion battery taking the core-shell structured carbon as the cathode material and a preparation method thereof. The core-shell structured carbon comprises a hard carbon material serving as a 'core' and soft carbon 'shell' which is coated on the surface of the 'core'. On the one hand, the hard carbon material serving as the 'core' provides a large number of spaces for storing lithium and channels for lithium ions to move, and the energy density and power density of the material are improved, and on the other hand, the soft carbon 'shell' with a graphite structure ensures that the material has high coulombic efficiency and cycle performance, so that the lithium ion battery made of the core-shell structured carbon serving as the cathode material has high capacity, high power characteristic, high cycle performance and high first charge and discharge coulombic efficiency, the preparation method is simple, and the cost is low.