The invention provides a diopter-adjustable optical 
system for a helmet display. The diopter-adjustable optical 
system comprises a glasses-shaped lens and a 
relay lens set. The glasses-shaped lens is arranged before the human eyes, and the 
relay lens set is arranged between a micro-display and the inner surface of the glasses-shaped lens. Image light rays sent by the micro-display of the helmet display are transmitted to the inner surface of the glasses-shaped lens by the 
relay lens set, and then the glasses-shaped lens is used for reflecting the light rays to the human eyes. The 
relay lens set is used for imaging an image of the micro-display to the position between the glasses-shaped lens and the 
relay lens set, and the glasses-shaped lens is used for magnifying the 
real image into a 
virtual image before the human eyes. The distance between the 
virtual image and the human eyes is changed according to the vision level of a user through zooming of the 
relay lens set, and therefore people with the normal eyes, the myopic eyes and the hypermetropic eyes can clearly see the image of the micro-display. Imaging and zooming of the relay lens set can be achieved by adopting six lenses, the complex degree of the relay lens set is reduced, and the structure is simplified.