The invention belongs to the chemical engineering field, and specifically relates to a coal syngas circulation gas free methanation technology. The technology firstly divides a methanation reactor into two parts, the purified raw material gas is divided into a plurality of gas flows, then the gas flows is introduced into the front methanation reactor, wherein parts of the front methanation reactor are connected through a combination mode of serial connection and parallel connection; the gas in the each level of methanation reactors in the front part goes out from the outlet of the first reactor and the outlet is serially connected to other level methanation reactors, or the gas is divided into a plurality of gas flows and enters other level reactors which are connected through a combination mode of serial connection and parallel connection. The technology adopts water steam as the diluting gas for diluting the raw material gas in a methanation reactor, the water steam is mainly applied to the high temperature methanation reaction technology, the pressure of the by-product namely steam is larger than the methanation reaction pressure, and thus the steam can be directly added into the raw material gas in a methanation reactor. The technology does not need a circulation gas compressor, so the production cost is reduced. Because the methanation reaction is a strong heat dissipation reaction, the added water stream is reduced so as to improve the energy utilization rate.