Abstract: Measurements of diffuse radiation fluxes at different slanting and azimuth angles have been made under various sky conditions by means of a pyranometer combined with a modified old-fashioned theodolite at Nanjing and in the Dabie Mountains in January, April and July. The data obtained are used to investigate the dependence of diffuse radiation on different slopes and azimuthes and evident anisotropy of its distribution is found. Besides, an attempt has been made to evaluate some of the models available for estimating slope diffuse radiation. A model developed on this basis is presented for this purpose. The comparison shows that the results given by this model are considerable better than those by the others. The accurary reached by this modelling approach is found sufficient for a wide range of applications.