The helmet-mounted sight/display system (HMSDS) is a typical man-machine interaction system that has significant advantages in utilization. Since the HMSDS is a complex head-borne vision equipment, it may make the users feel uncomfortable or even cause danger to them if it is not designed properly. In this paper, the operational tasks of HMSDS are analyzed, the existed problems of human/system performance are pointed out, and a man-machine interaction model is proposed. The methods for man/machine perfomance design and key factors that should be taken into consideration are presented in the end.