Abstract: A fast prediction method is presented for the full-space bistatic scattering sound field of the underwater stiffened double cylindrical shell. The scattering sound field is represented as the product of the acoustic scattering transfer function and the sound source density function. The target surface grid information and a small amount of simulation or experimentation multistatic scattering sound pressure data are used as known information to forecast other bistatic scattering sound fields with the help of numerical integration, matrix theory, and least squares method. The scattered sound pressure data from simulation of the finite element method (FEM) and experimental tests are used as input to calculate the multistatic scattered sound field of the underwater stiffened double cylindrical shell, respectively. The calculated results are compared with those calculated exclusively by the FEM, and the effects of different input data and calculation frequencies on the calculation results are discussed. The results show that the proposed method can predict the full-space bistatic scattered sound field of the target when the surface structure and part of the scattered sound field data are known. The greater amount of known scattered sound pressure data and lower computational frequency lead to higher prediction accuracy.