With the rapid development of China’s low-altitude economy and the planning requirements outlined in the “14th Five-Year Plan”， low-altitude transportation is expected to become a significant mode of transport. However， the current low-altitude airspace remains largely undeveloped and not fully open in China. As a result， related studies on airspace and trajectory planning are still in their early stages， and are difficult to meet the surging demand for low-altitude operations. Therefore， it is essential to establish a robust and comprehensive theoretical framework for airspace and trajectory planning according to the unique characteristics of low-altitude environments. This paper firstly examines the fundamental characteristics of low-altitude airspace and systematically reviews the research on the limiting factors of low-altitude airspace planning， airspace designation， and trajectory planning both domestically and internationally. Existing findings and gaps in current research are discussed， and common challenges in the field are also highlighted. Next， the feasibility of employing block or tube airspace designation methods is assessed in the context of China’s current low-altitude development. A developmental trajectory that evolves from individual trajectories to trajectory clusters and ultimately to trajectory networks is proposed， emphasizing the need for accelerated technological integration to innovate airspace infrastructure. Finally， this paper outlines three key elements that should be prioritized for future low-altitude airspace and trajectory planning： first， incorporating environmental and social factors as central elements in airspace planning； second， exploring phased airspace designation， composite designation strategies， and specialized planning methods； third， designing generalized fast algorithms for trajectory planning to accommodate diverse operational scenarios.