This paper aims to solve the problem of the oxygen cylinder contribution to the overall scattering intensity of the open breathing diver, which is the basis for mastering the accurate prediction and identification of the diver. A two-dimensional finite element axisymmetric model of 3D-object with non-axisymmetric excitation is constructed. The numerical solution to the far-field frequency characteristics of the acoustic scattering by the object with different azimuths is obtained by using the acoustic-solid coupling multi-physical interface in frequency domain. The reason and the estimation formula of the bright fringe at the resonance frequency are given. Under the assumption of the linear acoustics, the numerical solution to finite element method (FEM) is taken as the system function, and the linear frequency modulation signal with the same bandwidth is taken as the input signal of the system. The echo simulation in time domain can be obtained based on the convolution theorem. Combining the bright spot model and the elastic circumferential wave theory, the precise prediction model of the distance-angle echo in time domain is proposed. The results show that the main factors that affect the strength of the echo include the mirror reflection and the angular reflection. The additional bright spots and circumferential waves generated by the fine structures such as valves and spherical cap have a non-negligible influence on the frequency response characteristics in different azimuths. The validity of the echo prediction and resonance frequency characteristics is verified by the lake experiment in monostatic mode.