Abstract The Accelerator Driven Subcritical Reactor System (ADS) has a strong ability to transmute minor actinides (MAs) and it has inherent safety because of its subcritical core. However, the removal of decay heat is a major problem for the ADS and the design of spallation target is still a difficulty. Therefore, this paper presents a design of gas-cooled ADS with passive safety to attain the good performance of removing decay heat and transmutation. For the design of the target, the helium-cooled tungsten target is decided to adopt, and it is modelled into the cone structure to strengthen the convective heat transfer. A series of numerical experiments have been made to determine the optimal parameters of the target using the MCNP and CFX code. In the design of core, the subcritical core is divided into fast neutron region which the MAO2 is placed in and thermal neutron region which the UO2 is placed in to improve the performance of the transmutation. Two methods are proposed in this paper for the thermal-hydraulic calculation in the steady-state analysis, and the results show its good thermal performance.