The invention discloses a semi-coke and low-rank coal time-phased modification and steel heat supply coupled system. The semi-coke and low-rank coal time-phased modification and steel heat supply coupled system comprises a coal storage bin; an output end of the coal storage bin is connected with a first rotary kiln, an output end of the first rotary kiln is connected with a second rotary kiln through a material pipeline, and a discharge port of the second rotary kiln is connected with a cooling tower through a material pipeline; smoke outlets of the first rotary kiln and the second rotary kilnare respectively connected with a smoke inlet of a boiler; the first rotary kiln and the second rotary kiln are respectively heated by a heat accumulating type hot gas furnace and a heat accumulatingtype burner; a steam outlet of the boiler is connected with an urban heat supply system, and a flue gas outlet of the boiler is sequentially connected with a denitration device, a desulfurizing tower, a bag-type dust collector, an induced draft fan and a chimney. According to the system, in the process of preparing the clean solid fuel, the energy utilization rate is higher, and the system is more environmentally friendly and free of pollution.