Abstract: The wake of single vapor bubbles is a key factor affecting the flow regime formation and the evolution of vapor-water two phase flows in narrow channels. The wake of single vapor bubbles were examined under subcooling conditions in a narrow rectangular channel using Particle Image Velocimetry and post processed software Insight3G. Results showed that the wake structures were asymmetric with the vortex shed alternately in bubble rising process. The larger the bubble is, the stronger and the longer the vortex and the vortex strength are. As a result, the wake of large-diameter vapor bubble has a stronger effect on the surrounded bubbles become stronger. When the channel gap decreases, the strength and fluid velocity of the wake weaken, so as to the influence on the surrounded bubbles. Wake characteristics of single vapor bubbles can provide basic support for two phase flow model construction in narrow channels.