With the acceleration of the low altitude airspace opening process， the importance of low-altitude air route planning gradually appears. Air routes could ensure the safe and efficiency for aircrafts operation. However， there is no unified specification of low-altitude air routes planning at present， which lags behind the increasing demand in the future. Therefore， a complete and reasonable low-altitude air route planning system must be constructed. Based on the concepts and the development of low-altitude route planning， this paper focuses on the studies world-wide on urban air routes concept， air routes network design and construction， airspace structure and capacity. Then， according to the characteristics of airspace management in China and the future trend， the framework system of urban low-altitude air routes planning is proposed based on the theoretical research of airspace planning， infrastructure construction， air routes construction and operation evaluation. Finally， the challenges of urban low-altitude air routes planning development are analyzed.