The invention discloses an ultrahigh-temperature gas cooled reactor coupled iodine-sulfur circulation thermoelectric hydrogen cogeneration system which comprises an iodine-sulfur circulation hydrogen production module, a process heat extraction module, a power generation loop, an ultrahigh-temperature gas cooled reactor and an intermediate heat exchanger, the power generation loop comprises a steam generator, a high-pressure cylinder, an intermediate-pressure cylinder and a low-pressure cylinder, the high-pressure cylinder exhausts steam to supply heat to a hydroiodic acid decomposition preheater, and the intermediate-pressure cylinder exhausts steam to supply heat to a hydroiodic acid decomposition preheater; and steam extracted by the low-pressure cylinder supplies heat to the sulfuric acid purification tower, the sulfuric acid concentration tower, the hydriodic acid purification tower and the hydriodic acid rectification tower. High-temperature helium at an outlet of the ultrahigh-temperature gas cooled reactor transfers heat to secondary side helium through the intermediate heat exchanger, and the secondary side helium supplies heat to the sulfuric acid decomposer, the hydriodic acid decomposer and the steam generator. The ultrahigh-temperature gas cooled reactor and the iodine-sulfur cycle are coupled in the combined heat, power and hydrogen production system, heat, power and hydrogen can be produced at the same time, gradient utilization of energy of the ultrahigh-temperature gas cooled reactor is achieved, multi-level energy requirements are met, the overall energy utilization rate of the system is increased, and a basis is provided for design of a process heat utilization system of the ultrahigh-temperature gas cooled reactor.