Based on the smog full-screening detection system, the total obscure power of normal yellow phosphorus smog in 0.38～0.76 μm visual band was measured, and the variation of the smog grain size with time was also measured with granulometry. According to laser transmission model, a total obscure power (TOP) theoretical calculation mode was established under the condition of single-decentralization spherical particle. With the mode, the TOP values of various grain size yellow phosphorus smog with absorption index were deduced, and the theoretical calculation results were agreement with the experimental results. According to the experimental results, under a middle humidity and room temperature, the particle diameters were about 0.5～3 μm and gradually decreased after forming the smoke for 10～30 s, and the TOP values reduced with the diameter decrement.