Due to the substantial and continuous growth of transportation demand in China, the existing highway capacity has become insufficient to meet the increasing traffic volume. The implementation of highway reconstruction and expansion projects has gradually become a key measure to improve the service level of the road network and alleviate traffic congestion. Meanwhile, route design is a core aspect of highway reconstruction and expansion projects, and its scientific nature and quality can directly affect the safety, economy, and future operational efficiency of the highway. Therefore, this article provides a detailed analysis of the principles and requirements of route design for highway reconstruction and expansion projects. Additionally, it delves into the design process and key technologies applied in route design for these projects.