Abstract: Solar radiation is the main source for heating of thermosphere. The change of its intensity can result in the change of Earth's upper atmospheric density. With the same reasons, the difference between the sunshine and shaded area is one of the main reasons for the difference of upper atmospheric density at the same altitude. For Low Earth Orbit (LEO) orbiter, when running around Earth, it will pass the sunshine area and shaded area each orbit even the orbit is circular or quasi-circular. Theconsequent change of atmospheric density directly influence orbiter's motions and the precision of prognostication of orbit. On the other hand, change of atmospheric density resulted from sunshining and shaded area has something to do with different factors of solar-terrestrial physics, some discussions are needed, takeing into about these related phenomena. Although data of American earlier balloon detection had already been applied to the discussion of diurnal-change of upper atmospheric density, due to limitation of the conditions at that time, detailed description of the change could not obtained. And the later AE, DE satellite etc. all run at elliptical orbits, could not provide data for the discussion of the phenomena above mentioned. In this article, we applied the data from "SZ-2" Atmospheric Density Detector, which are the direct measurement results at quasi-circular orbit and very helpful for the discussion of atmospheric density change in sunshine and shaded area. We separate the results and primary analysis into 2 parts: Characteristics of Change and Response to Solar and Geomagnetic Activity, and will describe them seperately. This paper is mainly concentrated on the first part. "SZ-2" Atmospheric Density Detector started orbitting around the earth on January 18, 2001. The orbital inclination was 41? and the flew altitude was ⁴10 km. During the period of half a year, a lot of data of the upper atmospheric density have been obtained. In this paper, data of thermosphere density from February to April, 2001 collected by "SZ-2" Atmospheric Density Detector are used to study the change of the thermosphere density in the sunshining and shaded area. The results show that the ratio of the changes can be up to 2-3 in the vicinity of 410 km, and the magnitude of this change decreases as the geomagnetic activities increases. The peak value of the density in sunshining area increases as the solar activities increases and locates at the Local Time 14-15 h. The density in shaded area bear a relation to the geomagnetic activites, and increases as Ap value increases. The minimum value of the density in shaded area locates at the Local Time 4-5h. The latitude range of ?0?in the shaded area often show a density peak.