Abstract: Fuel of aqueous homogeneous reactor (AHR) is in liquid state and serves as both fuel and moderator. Radiolytic gas bubbles are generated by collision between water molecules and fission fragments. Bubbles’ existence and movement in the fuel make AHR’s transient neutronics simulation difficult. In this paper, a coupled neutronics and thermal-hydraulics method was introduced to recognize gas bubbles’ behavior; then a simplified gas bubbles model was established to make an effective simulation of gas bubbles distribution; finally the simplified model was applied to transient neutronics model of AHRs. The results show that the gas bubbles’ behavior accords with simulated results of coupling.