The invention discloses a pyrolytic poly-generation method of low-rank coal and a system. The system comprises a low-temperature dry-distillation unit (1), a crude-gas hydrogen extracting unit (2), a cooling and purifying unit (3), a tar hydrogenating unit (4), a high-grade solid fuel comprehensive utilization unit (5) and a crude-gas comprehensive utilization unit (6), wherein the cooling and purifying unit (3) is respectively connected with the low-temperature dry-distillation unit (1), the crude-gas hydrogen extracting unit (2), the tar hydrogenating unit (4) and the crude-gas comprehensive utilization unit (6); the low-temperature dry-distillation unit (1) is connected with the high-grade solid fuel comprehensive utilization unit (5); and the crude-gas hydrogen extracting unit (2) is respectively connected with the tar hydrogenating unit (4) and the crude-gas comprehensive utilization unit (6). The pyrolytic poly-generation method disclosed by the invention has the advantages that the idea of gradient utilization of graded substances of the coal is complied, the heat-energy conversion efficiency of pyrolytic poly-generation of the coal is high and can reach more than 85%. In addition, poly-generation products of the invention are rich and comprise power, methyl alcohol and synthetic ammonia and the like.