Determining ground motion duration is an important factor in the seismic analysis of structures as it has a significant impact on low-ycle fatigue, the cumulative effect of damage, and the inelastic failure of structures. In this paper, after determining the significant and Bolt durations, we introduce the concept of rotation-invariant mean duration. Then, based on Wenchuan seismic records, we discuss the spatial variability law of rotation-invariant mean duration with changes in the fault distance. Lastly, we analyze the ratio of the rotation-invariant mean duration and record-based duration of the measuring points as well as their correlation. The results indicate that the rotation-invariant mean duration is not equal to the single record-based duration. The rotation-invariant mean energy duration and relative Bolt duration increase with increased fault distance, whereas the rotation-invariant mean absolute Bolt duration decreases with increased fault distance. The rotation-invariant mean duration and record-based duration are highly correlated. By comparing different definitions of duration, we found that the correlation between rotation-invariant mean duration and a record-based duration of 90% energy is stronger than that of 70% energy. Furthermore, the correlation with the absolute Bolt duration is more significant than that with the relative Bolt duration, and the correlation with energy duration is more significant than that with the Bolt duration.