Abstract: With the rapid development of general aviation, the low-altitude airspace is emerging as a new growth engine for the global economy. Enhancing operational efficiency while ensuring safety has become an imperative. The integration of Communications, Navigation, and Surveillance (CNS) technologies is key to achieving safe and efficient operations. This paper comprehensively summarizes the CNS challenges in the complex, dynamic, and high-density low-altitude environment, with a focus on current development bottlenecks. It further explores innovative directions and application prospects for these technologies, aiming to lay the groundwork for breakthroughs in low-altitude CNS systems and their industrial implementation.