In order to quantitatively describe the correlation between drivers' visual search behavior and highway horizontal alignment, the study of drives' visual search behavior based on eye movement experimental was carried out. Firstly, the eye movement indexes under different highway horizontal alignment conditions were obtained by laboratory test; Secondly, the correlation between drivers' visual search behavior and highway horizontal alignment were analyzed from macroscopic level to microcosmic level. Finally, the laboratory testing' effectiveness and the results' reliability were verified by outdoor testing. The results show that the index of fixation duration has significant difference under different horizontal alignment condition. Moreover, drivers' fixation duration has remarkable correlation with horizontal radius R and the value of A. Using Lagrange mean value theorem, it is found that drivers' visual search behavior will change obviously when radius is greater than 1. 5 km or when distance between line section and curve section is less than 100 m. It would be a crucial point in drivers' visual search behavior.