The invention discloses a focal plane adjusting mechanism used for a star map display device of a dynamic star simulator. The focal plane adjusting mechanism is composed of a fastening screw, an outer sleeve I, a compressed spring, a stopping column, a connecting screw rod, a guide screw, a focus adjustment hand wheel, a limiting stopping ring, a radial adjustment gasket I, an adjusting screw, a radial adjustment gasket II and an outer sleeve II. By rotating the focus adjustment hand wheel, the connecting screw rod generates continuous axial displacement, so that a focal plane adjusting method without the steps of rotating a collimating optical system and rotating the star map display device is realized, and continuous radial and axial position adjustment can be carried out on the star map display device.