Based on the angle hole burning model, the transmission characteristics and formation condition of spatial optical soliton through photoisomerization are studied. Under the background light, the relationship between the refractive index and the light intensity is studied by MATLAB. According to the change law of refractive index, the forming conditions of soliton are discussed. The results show that the refractive index change can be positive or negative with the background light, and the bright soliton and dark soliton can be formed.