On the basis of the Nonlinear Doubly Asymptotic Approximation (NDAA) considering the compressibility of the water, the paper deduces and establishes mathematical calculations of the water entry of a complex cylindrical cavitary structure. By comparing the results of numerical calculation with the experiment, the reasonability of the procedure was validated. This paper calculated the hydrodynamic loads and response of the structure falling into the water, analyzed the weak part of the structure.，and made a research on the surface hydrodynamic loads laws in different drowning angle The research results indicate that the loads of the structure have a non-linear relationship with the pitching angle at the range from 45°to 90°,and the dangerous working angle is somewhere near 75°.