Embodiments of the present invention provide a 3D display device and a 3D display system, the 3D display device, comprising: a reflecting unit, reflecting light incident thereon; a polarization display unit, formed at a reflected light emitting side of the reflecting unit, and the polarization display unit for displaying images, converting incident natural light into polarized light and transmitting or blocking light reflected by the reflecting unit; and a polarization direction adjustment unit, formed at a reflected light emitting side of the polarization display unit, for converting the reflected light emitted from the polarization display unit into two sets of polarized light with different polarization directions.