Based on the data from two automatic weather stations (AWS) with 4-layers of soil probes located at an elevation of 5,400m at the Northern slope of Mt. Nyenquentanglha (N) and at 4,720 m at Boji (B) in the northwest of the Nam Co lake, this paper analyzed the environment of the frozen ground around the lake basin. It concludes that from September 2005 to May 2006, the daily temperature and monthly temperature at the N were both lower than those at the B, however, amplitude of daily temperature at the N was smaller than that at the BJ. The freezing period of ground at the N is longer than that at the B. From September to next May, their air temperature lapse rate is 0.31℃/100 m smaller than that in the atmosphere. Results show alpine permafrost existed at the N by comparing monthly temperature with the Ando, Tibet. Heat conduction between air and soil and within soil at the N was faster than that at the B. During freezing period, a powerful relationship was found between the soil unfrozen water content and soil temperature, the unfrozen water content abruptly declined at 0～-2℃. The Diurnal variation of soil temperature is dramatic at the 0~40 cm depth, while no trend below 40 cm; so does soil unfrozen water content at 5 cm depth, no trend below 20 cm. Based on the close correlation between a soil freezing depth (D_f) and a cumulative frost temperature (T_g), the model was proposed as the following: D_f-n= 0.0016T_g+ 1.69 at the N and D_f-b= 0.002T_g+ 1.13 at the B, using the model, the maximum freezing depth were estimated by 1.69 m and 1.13 m at the two sites, respectively.