Abstract: The conception and connotation, assessment indicator system, mechanism of desertification occurrence, as well as the relationship between the land use/land cover change in desertification affected area and desertification were discussed tentatively. The definition of desertification in “United Nation Convention to Combat Desertification in Those Countries Experiencing Serious Drought and/or Desertification. Particularly in Africa”(hereinafter referred as CCD), from the author’s point of view, revealed the general intrinsic property of all types of desertification with different causes. The definition of desertification in CCD, therefor, represented the scientific connotation and was acknowledged worldwidely. The “Bench Mark" of assessment indicators, the climatic types and the areas in which the desertification occurred and the spatial scale of assessment should be taken into account when establishing the assessment indicator system of desertification. The mechanism of desertification occurrence is a core issue of desertification research. It involves the feedback courses and the nonequilibrium processes in desertification,as well as the relationship between the biodiversity,complexity and the stability of land ecosystem. Finally, the relations of land use/land cover change(LUCC)to desertification were discussed. It was pointed out that LUCC was one of the driving forces of desertification.