Abstract: To analyze the sound radiation problem of an orthogonally stiffened plate, a theoretical model is developed to investigate sound radiation characteristic of the orthogonally stiffened panels based on the direct solution method in wavenumber domain. Fourier transform method is firstly employed to solve the vibro-acoustic theoretical model of the periodic structure, and then an infinite set of simultaneous algebraic coupled equations about the response of the structure in wavenumber domain is got, which can be numerically calculated by truncating them in a finite range. Finally, the far field radiated sound pressure is determined quickly combined with the stationary phase method. As a result, the validity and feasibility of the present model is performed by comparing the predictions of single and orthogonally stiffened panel with existing results, and perfect agreements are achieved. Furthermore, numerical examples are presented to investigate the effects of the excitation locations, the periodicity spacing and inertia moment of the stiffeners on the sound radiation characteristic of the orthogonally stiffened panel.