Abstract: The advent and development of portable consumer-grade cameras accelerate the use of depth information in many application fields, such as autonomous navigation, human computer interaction, and 3D reconstruction. However, depth images captured by these low-cost cameras usually have very low spatial resolutions. Depth image super-resolution (DISR) is an effective way to improve the spatial resolution of depth information, which has been a research focus in computer vision and image processing fields. The concept and necessity of DISR are described in detail in this paper. In addition, the DISR methods in recent years are comprehensively reviewed from the perspective of input image. Some of the key technologies and the development trend are analyzed. And the application prospect of DISR are provided at the end of this paper.