Abstract: The Boundary Element Method is a classical method to numerically evaluate the scattering property. However, its accuracy usually degenerates when sound waves impinge on diffusers in an grazing angle. In order to improve the simulating accuracy for grazing incident waves, a Boundary Meshless Model which is applicable to diffusers with arbitrarily shaped surfaces is proposed. In the model, diffusers are assumed to be attached on infinitely extent walls, which avoids the problem of the sound pressure difference caused by the form of thin plate in traditional Boundary Element Method. The meshless method is used to implement numerical calculations, which contributes that the model is applicable to diffusers with rough surfaces, especially curved surfaces. The Boundary Meshless Model is then used to analyze the scattering property of diffusers in numerical verifications. Comparisons of results with those obtained by the analytical method and measurement have proved that the model has higher accuracy than the Boundary Element Method on evaluating the scattering property for grazing incident angles. The method can be used to design the sound diffusers in architectures to promote diffusions and present echoes. It is potentially effective to improve the sound quality of the room.