A three-dimensional display device having an imaging space, wherein an up-conversion material is disposed inside the imaging space, a first light source that emits light toward the imaging space in a first direction, and a second light source that emits light toward the imaging space in a second direction. When the three-dimensional display device is operating, the light from the first light source and the light from the second light source intersect in the imaging space to form a convergence line or light convergence plane, such that the up-conversion material on the convergence line or in the convergence plane is excited to emit light.