Abstract: Based on Kulenkampff empirical formula about X-ray intensity, an approximate numerical algorithm for X-ray intensity and its attenuation characteristics in industry radiographic testing is provided. Using Newton-Cotes numerical computing algorithm, combined with Matlab soft programming, for steel material and in different energy X-ray, the X-ray absorption curves of relative intensity against material thickness, mean attenuation coefficient, half-value thickness and their variation curves are obtained, and confirmed to the X-ray attenuation theory. By comparison with analytic algorithm in T=0, the error of the approximate numerical algorithm is below 3%, which can meet the requirement in radiographic testing. The study results show that the numerical algorithm used in this paper has universality and practicality, and can implement effective analysis theoretically on X-ray attenuation in various materials during radiographic testing.