This paper described the methods of measuring the powder concentration with scattering theory. We mainly discussed and compared the measuring methods with the extinction theory and Mie theory. Compared with the result which was worked out with the powder particles whose size are single, we analyzed the result worked out with the powder particles whose size obey some function. The Rosin-Rammler function is introduced to describe concentration and mean diameter. The difference between these two results was disussed. Then we simulated the result about coom by computer. The result is shown by the chart given.