The precipitates size distribution and morphology in an Al-Zn-Mg-Cu-Li alloy are studied by small angle X-ray scattering and transmission electron microscopy. The results show that the precipitates belong to ellipsoid and their axis ratio range is between 0.2 and 0.4, aged under different conditions. The logarithm Gaussian distribution of effective size and the Maxwell distribution of particles mass with gyration radius are also constructed. The changing of both types of distribution curves with kinetic strength Ks has been analyzed.. The results show that the geometric average and distribution width for both types of distribution curves increase with kinetic strength.