The invention provides a low-rank coal low-temperature dry distillation pyrolysis process at the aim of existing problems of resource waste, high energy consumption and a large amount of pollution discharge of low-rank coal including lignite and the like. The process adopts an improved multistage furnace as carbonization equipment, gas obtained from low-rank coal material subjected to pyrolysis and oil extraction as a circular heat carrier, and the low-rank coal is subjected to drying, preheating, carbonization, pyrolysis, tar extraction and semicoke production. According to the process, the low-rank coal including the lignite is conveyed to a multistage furnace via a hopper above the multistage furnace, under the pushing action of the harrow teeth in the multistage furnace, the material is uniformly pushed and turned on a furnace layer surface, and is lowered from a drying section, a preheating section, a carbonization section and a cooling section in sequence; via the drying, preheating, dry distillation pyrolysis, thermal oil gas and semicoke are obtained; the thermal oil gas upwards flows through the preheating section, the drying section and a diffuse section and then is exhausted out of the multistage furnace, tar and gas are obtained via extraction, and the gas is reused as a heat carrier. As a result, the scientific and comprehensive application of the low-rank coal is achieved.