To study the relationship between the tower controller’s SA and their fixation mode at different stages of the task, an eye-tracking experiment platform to simulate the tower control was built. Three group experiments of varying task difficulty were designed, and NASA-TLX scale was utilized to evaluate the subjects’ workload. Through variance analysis, the result showed that the experiments designed were validated be reasonable. 3D-SART scale was utilized to evaluate the subjects’ SA, and NNI algorithm was utilized to calculate and identify the subjects’ fixation mode at pre- and post- experiment stage. Combined with operation performance, the relationship analysis of pre-and post-NNI fixation index and SA under different task difficulty were carried out. Results reveal that post-NNI fixation index was affected more significantly by varying experiment difficulty, and the subjects whose post-NNI fixation index showed a discrete distribution have higher levels of SA and better operational performance.