Abstract: In the nuclear power plant, a large-break loss-of-coolant accident may induce a transition of the coolant flow regime into a high void fraction condition, such as the annular flow. The stability of disturbance waves in annular flow directly influences the safety margin of the reactor system under accident conditions. The spatial distribution characteristics of disturbance waves were investigated in gas-liquid annular flow within a rod bundle channel, providing insights to support reactor safety analysis and accident mitigation strategies. An experimental system was established with a 3×3 rod bundle channel, and a high-speed camera was employed to record the interfacial wave behavior and extract the spatial data of wave height. Three-dimensional transient numerical simulations were performed using the validated SST k-ω turbulence model coupled with the volume of fluid (VOF) method, so the detailed distributions of the two-phase velocity field and turbulent kinetic energy were presented. Based on the experimental and simulation results, a systematic analysis of the disturbance wave propagation mechanism was conducted. The results show that the wave height increases gradually along the axial direction, exhibiting a three-stage developmental pattern: the initial coalescence region, the merging transition region and the stable propagation region. The initial coalescence region is dominated by a number of small-scale waves with low wave height. In the merging transition zone, the aggregation frequency of wavy structures increases, leading to a gradual rise in the number of large-scale waves. In the stable propagation zone, the wave height is almost constant, and the large-scale waves are more numerous, which contribute the most to the overall wave height. The wave height decreases successively from the corner rod, to the side rod, and finally to the center rod. This pronounced non-uniformity arises from the local geometric features of the subchannels. Increasing the gas flow rate and decreasing the liquid flow rate result in the wave height growth, with the liquid flow rate exerting a more significant influence across all test conditions. The distribution of disturbance waves is governed by the balance among inertial forces, interfacial shear, and turbulent kinetic energy. The turbulent kinetic energy serves as the key energy source for wave amplification in the subchannels with wider space, while the strong turbulent dissipation combined with geometric constraints jointly inhibits wave height development in narrow gap regions. These results provide a theoretical basis for refining subchannel analysis models and for optimizing the safety-related design and operational measures of nuclear reactor components.