Abstract: A method based on six-parameter rectangular coordinate transformation which is propitious to measure submarine's pressure hull radial initial deflection is presented. It resolves the problem that traditional seven-parameter bursa mathematical models are unsuitable for large-rotation-angle cases and rely most on the initial value that could lead to large coordinate conversion deviance. To do so, the six-parameter rectangular coordinate model is first adopted to be derived on the basis of complete coordinate transformation formulas. Then, the computational process is enhanced with the improved Gauss-Newton method. Finally, the proposed method is realized by the MATLAB program. Using the analog data and actual project data, a comparison between the traditional bursa mathematical model verifies the accuracy and stability of the proposed algorithm.