Abstract The polarization basis misalignment caused by polarization fluctuation is the main limiting factor in the deployment of polarization-encoding quantum key distribution (QKD) in aerial fibers. In this study, we conduct further research on polarization fluctuations in aerial fibers from the perspective of QKD. We propose a method to evaluate polarization fluctuation in aerial fibers. The relation connecting the quantum bit error rate (QBER) to the components of the Stokes vector is derived. Through a field experiment, long-time data on the polarization fluctuations in a 68-km-long aerial fiber are obtained. A statistical analysis of the time-cost corresponding to a typical QBER caused by polarization misalignment is conducted. The results can be used to evaluate the required speed of polarization compensation, and they indicate that the time-cost of the polarization compensation module should ideally be lower than 1 ms. This can provide guidance for the design of polarization compensation modules and algorithms for polarization-encoding QKD systems based on long-distance aerial fibers, aiding in its deployment.