With the increasing share of renewable energy generation in power systems, its intermittency poses new challenges to the transmission capacity of traditional power grids. Dynamic line rating (DLR) technology offers a new approach to address this issue without modifying existing transmission lines. Implementing DLR requires the installation of sensors to monitor ampacity. However, due to the long spans of transmission lines, installing sensors along the entire line would lead to excessive costs. Therefore, to ensure accurate ampacity monitoring while reducing sensor deployment costs, it is necessary to optimize the monitoring positions and reduce the complexity of the monitoring system. This paper proposes a method for selecting monitored spans and evaluates its effectiveness.