Abstract: According to the construction requirement of China Initiative Accelerator Driven System (CiADS), a conceptual design of subcritical reactor in CiADS was completed. The subcritical reactor is a liquid lead-bismuth cooled fast reactor with the semi-pool semi-loop type arrangement mode, and the center tube in vessel was used to realize the structure coupling with the spallation target. The relatively mature fuel scheme and refueling pattern were adopted, the unique lead-bismuth coolant auxiliary system was designed, and a variety of engineering safety systems were set up to ensure the safety of the reactor. In the design of the CiADS subcritical reactor, the feasibility of the reactor-target interface is fully considered, and the favorable heat transfer capacity of the liquid lead-bismuth is utilized. The natural circulation capacity characteristic of the pool-type reactor and low coolant capacity characteristic of the loop-type reactor are realized together. The good feasibility, safety, arrangement flexibility and technical scalability are combined in the CiADS reactor design.