Visual information is the basis of highway traffic safety, which is important for a driver to take right actions in driving. From the driving theory and the driver’s sight characteristics, the concept of available sight distance is put forward. According to extend and apply the theory of the spatial intervisibility between two spots, the math model of calculating and analyzing the spatial available sight distance is built up, which is solved by use of parameter equations and space conversion. On the basis of this model, the safety evaluation model and the evaluation procedures are given. At last, the effectiveness of the model is tested in practical engineering applications, and it can provide the basis for highway geometric design and safety evaluation.