The invention belongs to the fields of energy and chemical industry and in particular relates to a trickle-bed reaction device and a trickle-bed reaction process for synthetic gas methanation. An inert heat carrier medium with the advantages of high heat capacity, high heat conductivity coefficient, high stability and low mass transfer resistance is introduced into a common gas-solid catalytic fixed bed methanation reactor, and a trickle-bed gas-liquid-solid three-phase methanation reactor is formed. Lots of reaction heat is absorbed and transferred by utilizing the high heat capacity and good heat-conducting characteristics of the inert heat carrier medium, the product yield is improved, the carbon deposit phenomenon in the reaction process is relieved, and catalyst inactivation is delayed. The advantages of the gas-solid catalytic fixed bed methanation reactor and a slurry bed methanation reactor are integrated, the respective disadvantages of the two reactors are avoided, and the problem that the reaction heat is difficult to remove and utilize due to strong heat release characteristics of the methanation reaction system is solved under the condition that high operating air speed and product yield are guaranteed. Meanwhile, the catalyst collection and separation equipment is saved, the operating cost is saved, and the economical efficiency in the process is greatly improved.