Abstract: For the years from 2001 to 2013, the atmospheric densities and temperatures in the transition flow region of east and central China are simulated by the US Naval Research Laboratory Mass Spectrometer Incoherent Scatter (NRLMSISE-00) model, with the space environment indices including 10.7 cm solar flux and the geomagnetic activity index Ap) as the external forcing factors. The simulation results are analyzed. Variations of monthly averaged densities and temperatures from different reference sites agree well with each other. The semiannual variation of the atmospheric density above 90 km is found from spectral analysis. The amplitudes of the semiannual variation increase with the increase of the latitude between 90 km and 110 km. From the spectral results, the maximum and minimumdensities of the first cycle of the semiannual variation are found, respectively, in March and June at 100 km, which is significantly earlier than the previous results of the middle and upper thermospheres.