With the continuous reforms of low-altitude economy， the advancement of low-altitude aircraft are presenting a new landscape characterized by high density， heterogeneity， autonomy， and mixed manned/unmanned operations. Low-altitude surveillance， as an important safeguard for the safety of low-altitude operations， can ensure the safe and efficient operation of aircraft at low altitudes. To address current issues of inadequate low-altitude surveillance means， it is necessary to construct a low-altitude surveillance technology system with no blind spots， covering mixed manned/unmanned operations， based on the characteristics of the complex low-altitude environment. Firstly， current difficulties in low-altitude surveillance are analyzed from the perspectives of the concept of low-altitude surveillance and its development trends， including weight， size and power limitations of airborne equipment， tight channel resources， and significant differences among aircraft. Secondly， from the perspectives of the cooperative surveillance technology and the non-cooperative surveillance technology， the current status of key surveillance technologies worldwide is elaborated， and a systematic comparison and summary of the relevant characteristics of each technology are provided. Finally， facing the development of a new generation of low-altitude surveillance， the development directions of future cooperative surveillance， non-cooperative surveillance， and integrated surveillance technologies are discussed， with the expectation of providing certain guidance for the safe operation of low-altitude aircraft in the future.