The definition of radiative function in atmospheric short wave radiation transfer was improved to include the variation of the product of atmospheric scattering phase function and atmospheric single scattering albedo with height.The properties of the improved radiative function (IRF) were studied, which include the relationship between multiple scattering light and IRF, the analytical recurrence formula of IRF, the analytical relationship betweem high order IRF and zero order IRF and the power series of IRF about optical depth.