In this study we obtained the tomography results of QLg in Sichuan‐Yunnan region, separately for each frequency, by using seismic wave data recorded by Yunnan and Sichuan seismic networks. The spatial resolution of our result is less than 100 km. Our results demonstrate that strong heterogeneity exists in the studied region, showing large difference between the highest and lowest Q value. The obvious high attenuation regions include the southeast edge of Sichuan‐Yunnan rhombic block, which extends from Xianshuihe fault zone to Anninghe fault zone, Simao‐Lancang‐Pu'e region, the Songpan‐Maowen region which is located to the west of Longmenshan fault zone, the Batang and Litang earthquake region. According to our result, high attenuation regions of Lg waves correspond to strong seismic active zones, ruptured area of large earthquakes, high terrestrial heat activity, and low velocity. It demonstrates that broken medium caused by strong tectonic activity or large earthquakes and heat flow upwelling along active faults may be the main reasons of low QLg in Sichuan‐Yunnan region. The obvious low attenuation regions include Sichuan basin, the eastern block of Yunnan region, and the middle part of Jinshajiang and Nujiang fault zones. The interior of Dianzhong block also shows lower attenuation than the nearby area. Low attenuation regions correspond to the stable tectonic block, weak tectonic activity and high velocity. It shows that low attenuation of Lg waves in Sichuan‐Yunnan region is correlated with small crustal deformation, low seismic activity, weak hydrothermal activities and stable block.