Abstract: The desertification process,with great controversy,is considered to be one of the main reasons to permafrost degradation in Qinghai-Tibet Plateau apart from the influence by climate change and anthropic activities. Previous contestable views include:(1)sand deposition accelerating permafrost degradation;(2)thin sand layer protecting permafrost while thick sand layer degrading permafrost;(3)sand accumulation protecting underlying permafrost regardless of its thickness. Though field investigations and laboratory simulative experiments have been carried out,it is still unclear what the influence mechanism between sand deposition and underlying permafrost is. This research developed a preliminary conceptual model and coupled hydrothermal modelbased on soil hydrothermal processes and also referred to two primitive models including CoLM and CoupModel. Importantly, these models contribute greatly to well understanding the influence mechanism of underlying permafrost covered by sand. Based on the two models,later analyses on the stability of underlying permafrost influenced by multi parameters of sand layer,such as reflectivity,thermal capacity,thickness and its thermal conductivity were carried out. Most of the analyses are qualitative descriptions and comparisons based on the conceptual model owing to the lack of data support. The energy caughtby sand layer is less than that in natural surface owing to the higher reflectivity and emissivity of sand layer.At the meantime,permafrost layer obtainedless thermal energybecause more energy was reserved by sand layer and the thermal conductivity was poor under sand covering surface,resulting in a delay of permafrost degradation. Additionally,sand layer would postpone permafrost degradation processes in spite of how thick the sand layer is. In conclusion,desertification should not be reckoned as the main reason of permafrost degradation in the Qinghai-Tibet Plateau,andmore attention should be paid on climate change andanthropic activities. In addition,the conceptual and physical models in this paper are innovated originally regarding to the stability of underlying permafrost influenced by sand covering,and it is also a creative idea that the physical model combines two common land process models. More endeavor need to be carried out on the further improvement of the physical model and numerical simulation and combination of the field observations and indoor laboratory experiments,to better understand the whole process of desertification and permafrost degradation. This research is meaningful in revealing the relationship between permafrost degradation and desertification, andcan provide references for the construction of important engineering projects passing sandy-permafrost belts on the Qinghai-Tibet Plateau or other similar areas.

Key words: Qinghai-Tibet Plateau, Sand accumulation, Permafrost, Coupled hydrothermal model