The invention relates to the field of lithium batteries, and discloses a graphene modified-carbon coated lithium iron phosphate material and a preparation method thereof, and a solid lithium ion battery, the preparation method comprises the following steps: dissolving a phosphate radical raw material, an iron salt and a lithium source in an alcoholic solution, then adding a template agent, a carbon source and an antioxidant, then adding graphene oxide, and carrying out ultrasonic dispersion, so as to obtain the graphene modified-carbon coated lithium iron phosphate material. Pouring into a reaction kettle, and carrying out hydrothermal synthesis to obtain a solid-phase material; and placing the solid-phase material in a vacuum oven for drying, and then placing the dried solid-phase material in a muffle furnace for high-temperature calcination to obtain the graphene modified-carbon coated lithium iron phosphate material. When the G/LFP/C material is applied to a solid-state battery, the transportation of electrons and lithium ions can be facilitated, and the interface impedance is reduced, so that the solid-state battery prepared from the G/LFP/C material can have excellent rate capability, electrochemical lithium storage performance and cycle performance.