The invention discloses a system and a method for natural gas production and hydrogen co-production through low-temperature dry distillation gas. The system comprises a low-temperature dry distillation poly-generation unit, a water washing purification unit, a hydrogenation unit, a fine desulfurization unit, a pre-conversion unit, a methanation unit and a pressure swing adsorption unit which are connected in series sequentially through inlets and outlets; low-rank coal conveyed by a coal preparation system is pretreated by the low-temperature dry distillation poly-generation unit and further purified by the water washing purification unit, all unsaturated hydrocarbons in gas are converted into corresponding saturated hydrocarbons through the hydrogenation unit, and organic sulfur is converted into H2S simultaneously; the content of H2S in feed gas is reduced to be lower than 0.1 ppm through the fine desulfurization unit; higher hydrocarbons above C2 in the low-temperature dry distillation gas is totally converted into methane with a pre-conversion process, and the utilization rate of carbon is increased; hydrogen co-production is realized, and the requirement for high-purity hydrogen during reduction of a methanation catalyst and a pre-conversion catalyst is met; efficient graded use of the low-rank coal is realized, and the process is simple and high in operability.