Abstract: An image-based method has been developed for measuring the instantaneous radial void fraction distribution in bubbly flows with higher void fractions in a vertical pipe.The method is based on the statistical analysis to shadow images of a bubbly flow,which were obtained using a stereo photographic tech-nique.The projection void fraction distribution was obtained,by counting all pixels of bubble shadow images and considering the overlapping probability of the bubble shadows.Then the instantaneous radial void frac-tion distribution in the bubbly flow was reconstructed from projection void fraction distributions on the as-sumption that the radial void fraction distribution is axial symmetrical.An improved algorithm for Abel inver-sion calculation has been proposed to reconstruct the radial distribution of the local void fraction based on the Fourier method.Finally,the method is checked for the accuracy in the measurement of the radial bubbles dis-tribution by comparing with the labeling method results.The comparison results showed that some special void fraction profiles,such as the wall-peaked or high void fraction distributions that usually cannot be ob-tained by other methods,could be measured by this method.