In this paper, a new method based on ray optics and Kirchhoffs method, using tangential plane approximation for calculating the scattered power from rough surface is proposed. Meanwhile applying the Kernel's approach together with the proposed model, the irregular plane parameters for different irregularities are calculated, and then the scattered power with respect to different elevation and azimuthal angles is estimated and compared with measured data, Kirchhoffs and stochastic scattering models. It is observed that there is good agreement between results obtained from the proposed model and measurements. Therefore, it can be concluded that using the proposed model to calculate the path loss in mobile communication leads to a better design and field estimation than Kirchhoffs or stochastic scattering models. Also in radar cross section estimation, the proposed model can assist us in calculating and estimating the maximum and minimum scattered power from rough surface with different degrees of roughness, which is important in radar cross section design and analysis. In addition, the proposed model in contrast to Kirchhoffs method can be applied to any surface with any distribution function and different degrees of roughness. Therefore, using the proposed model for calculating scattering power can lead to better results than Kirchhoffs or stochastic scattering models.