The measurement of particle density is affected by particle size and color in the optical method.The Kumbelka-Munk-Lu equations were built that contained the variables of particle density

size and color.The value of particle density affected by particle size could be derived by the forward scattering extinction equation of the Kumbelka-Munk-Lu equations; The scattering extinction coefficient

the absorption extinction coefficient and the effective optical density equation were given.The problem was solved that the Beer extinction equation was affected by particle size and density.The experiments were done to test the Kumbelka-Munk-Lu equations.