Abstract: The upper atmosphere of Mars has received more and more attention in recent years. Without the protection of a strong magnetic field, the Martian upper atmosphere is closely interacted with the interplanetary particles and fields. At the same time, the activities of the lower atmosphere (e.g. the dust storms) can also affect the structure of the Martian upper atmosphere. Furthermore, the ionosphere embedded in the upper atmosphere could make these relations and interferences more complicated. The variations of the Martian upper atmosphere and ionosphere have a great impact on the Martian exploration and telecommunication missions. However, with the observations of the Martian neutral atmosphere at a height of 100~130 km, the long-term and stable data are still not available. This paper reviews the evolution and the current state of the study of Mars’ upper atmosphere, as well as the methods of calculating densities of Mars’ 130 km-high neutral atmosphere through the MGS radio occultation observations. The main results are discussed and the future work is suggested.