Abstract: Window is one of the most important parts of a house to prevent noise from outside especially in the modern world surrounded by cars and other machines. The staggered-structure window system, which is constructed by staggering the external and internal openings of a double glazing, can provide the natural ventilation and the noise attenuation simultaneously. Because of its unique structure design, instead of directly going into the room, the noise has to pass through the channel comprised by the double glazing window and it is reduced by this way. The existing theoretical models are only applied in the investigation of the sound field in the normal incidence condition and the use of sound materials is out of consideration in these theoretical models. In this paper, a new acoustical model is presented to be suitable for the oblique?incidence plane wave, and its validity is proved by comparing it with the computation results of the FEM model. Incident sound, reflected sound and diffuse sound are all introduced to correctly and analysis the situation at the opening of the window. Coupled acoustics field analysis and modal superposition method are both utilized to study the sound field of all space and primarily focus on the sound field inside the window. Based on the proposed model, the sound field inside the natural ventilation window is studied with different incident angles and the influence of the sound absorption materials has also been taken into consideration. As a consequence, the sound field inside the window is influenced by the incident angles especially at higher frequencies. The sound pressure of different frequencies tends to be smooth with sound absorption materials of lager coefficient attached inside the window and some materials of different absorption coefficients can be taken use of to focus on some targeted frequencies when the window is applied in some areas. Difference of the sound pressures at the two openings can be calculated with this model and the size of the openings should be changed to get proper noise reduction as well as enough air exchange at the same time. The theoretical modal in the present research can be further applied for the location optimizations of the reference and error microphones during the realization of the active window.