The study of natural suitability of human settlements environment aims at objectively revealing the human settlements under the influence of natural geographic elements, which to quantitatively characterize the pattern of regional population distribution under natural limitations or suitability. Based on the kilometer grid, the study establishes the Human Settlements Index (HSI), which includes Relief Degree of Land Surface (RDLS), Temperature-Humidity Index (THI), Land Surface Water Abundance Index (LSWAI) and Land Cover Index (LCI). The main conclusions are as follows: (1) The RDLS of Qinghai-Tibet Plateau is dominated by high values (high elevation, sharp topographic undulation), with great regional differences. It is obviously different that the THI of the region, which shows an increasing trend from the northwest arid region to the southeast. However, both the high LSWAI and the LCI distribute on intensively and zonally. (2) Supposed that the auxiliary elements (hydrology, vegetation) enhance dominant elements (topography, climate), the conclusion shows that the HSI between 0.07~1 in the study area, averages 0.45. According to the grading judgment of the topographic and climatic suitability, with the restriction of physiological elements on human habitation, there defines the 7 types of human settlements environment suitability. (3) The unsuitable type account for 32.48% of the total area, and only 1.87% of the corresponding population, mainly distributed in the Kunlun mountains, the Gangdis mountains and the western side of the Himalayas. As an important basis, human settlements suitability provides scientific basis for resources and environment carrying capacity, moreover, it supports the regional planning and population distribution.