A wearable device, a 3D display system, and a 3D image displaying method are provided. The 3D image displaying method includes acquiring a curvature information of the 3D display device when the 3D display device is turned on; adjusting a curvature of the wearable device according to the curvature information; determining whether an adjusted curvature of the wearable device and a curvature of the 3D display device satisfy a predetermined relationship; and sending a control signal to the 3D display device to control the 3D display device to display a 3D image when the adjusted curvature of the wearable device and the curvature of the 3D display device satisfy the predetermined relationship.