Photodegradation of chrysene, benzo(a)pyrene and benzo(ghi)perylene in natural water of the Yellow River was studied using simulation sunlight. The effects of particulates on the photodegradation were explored. Several results arose from this study: (1) The photodegradation of PAHs can be fitted with first-order kinetics when no particulates exist in water system, and the first-order constant increase with the decrease of initial concentration of PAHs. The photodegradation rates of the three PAHs are related to their molecule absorption spectrum. (2) The presence of loess exerts two kinds of effects on the photodegradation of PAHs, which include the inner filter effects and the photosensitizing effects of humic substance in Loess. These two opposite effects lead to the difference of net effects among different contents of loess. When the loess contents are 0.1 g/L and 5.0 g/L, the presence of loess stimulates the photodegradation of chrysene, benzo(a)pyrene. When the loess content is 5.0 g/L, the presence of loess stimulates the photodegradation of benzo(ghi)perylene. In addition, the photodegradation of PAHs can be fitted with the second-order kinetics when there is loess in the water system. (3) The dissolvable humic substances in loess can accelerate the photodegradation of PAHs while the indissoluble part cannot. (4) Since the dissolvable humic substances in the suspended solids of the river have been dissolved in water, the addition of suspended solids to the water system can only cause the decrease of photodegradation rate of PAHs due to its inner filter effects, and the photodegradation rate decreases with the suspended solid content as a power exponent function.