Abstract: Natural ice nucleus in atmosphere are one of the basic conditions for the ice crystal formation, which can exert a key influence on the cold cloud precipitation. In addition, many researches on ice nucleus show that ice nucleus play the same important role in the various weather processes as the cloud condensation nucleus. Besides the influence on the microphysical structure of cold cloud and precipitation, ice nucleus concentration affects the radiation characteristics of cloud and then influences the weather and climate processes accordingly. In order to understand the physical mechanism of the precipitation and microphysical background of rainfall enhancement in China, the observation on ice nucleus is carried out and a lot of useful results are gained since 1960. However, up to now, most researches focus on different areas, the continuous observations on the same area, the same period and using the same method are few, especially over Tibet Plateau. To highlight the characteristics of the ice nucleus over Tibet Plateau area (Henan County in Qinghai Province), some useful results for the further understanding on the precipitation mechanism and weather and climate processes are provided. In terms of the Bigg mixing chamber in which the valid volume of the chamber is 3.05 liter the ice nucleus are observed from October 5 to 26 in 2003. On the bottom of the chamber, there is the sugar plate whose diameter is 10 centimeter. The super cold fog is formed manually, which can last 2—3 minutes. The ice nucleus form little crystals falling down to the sugar plate, increase until they can be distinguished by eye, then the sugar plate is pulled up to count the crystals number, so the ice nucleus concentration is obtained. This method is applied in the observation of ice nucleus over Tibet Plateau in the year of 1989, 2000, 2001, 2002. Also, the observations are compared with that gained in last two years in the target area and other plateau areas. Results show that: ① The concentration of ice nucleus over the plateau is greater than previous while the distribution slope is smaller, and the distribution of ice nucleus is inclined to evenness; ② The graupel and rainfall during night contribute to the uncertainty of ice nucleus concentration; ③ The relation between the concentration of ice nucleus and the pressure is negative while the relation between the concentration of ice nucleus and humidity is positive; ④ Wind influence on concentration of ice nucleus and the variety of ice nucleus in low temperature is larger than that in the high temperature; ⑤ Human activity may have influence on the concentration of ice nucleus.