An embodiment of the invention provides a 3D display device and a manufacturing method thereof. The 3D display device includes a display unit; and a birefringent grating stacked at a light emitting side of the display unit, wherein the birefringent grating including a concave lens film, and liquid crystal polymer covering the concave lens film, a long or short axis of the liquid crystal polymer being parallel to a ridge direction of the concave lens film, and a polarization direction of emitting light of the display unit is parallel to the ridge direction of the concave lens film of the birefringent grating.