The invention discloses a solar photocatalyst, as well as a preparation method and application thereof. The preparation method comprises the following steps: weighing Fe(NO3)3.9H2O and Na2HAsO4.7H2O respectively, loading Fe(NO3)3.9H2O and Na2HAsO4.7H2O in different flasks, dissolving Fe(NO3)3.9H2O and Na2HAsO4.7H2O with de-ionized water, and loading the solutions in two separating funnels respectively, wherein a proper stabilizer OA is added into the Fe(NO3)3 solution; preparing nitric acid at a concentration of 0.2 to 0.8mol/L with concentrated nitric acid; carrying out reaction between the Fe(NO3)3 solution and the Na2HAsO4 solution under a room temperature magnetic stirring condition according to a parallel flow precipitation method; controlling the pH of the mixture to be 2 to 4 by virtue of the nitric acid, and continuing performing magnetic stirring for 2 hours at room temperature under a dark condition after titration; washing prepared light yellow precipitates for many times, and drying the precipitates to obtain a light yellow powdery product, namely an FeAsO4 solar photocatalyst. The solar photocatalyst is applied to the degradation of organic pollutants under visible light. The preparation method is extremely simple and favorable for large-scale popularization and application, and the conditions are mild and easy to control.