Abstract: The roundness of the pressure hull is an important indicator for ensuring comprehensive strength. As such,a calculation method for pressure hull radial initial deflection based on the three dimensional point cloud is proposed. The method obtains the initial deflection of the given frame by feature point extraction,projected profile and circle-fitting based on the obtained spatial point cloud. It resolves the problem of the traditional initial deflection method being inefficient and unable to reflect the overall situation. The experiment shows that the results of the initial deflection obtained by the new method are the same as those of the traditional method,suggesting that it can effectively increase measuring efficiency.