Abstract: In this research, we derived TLE-based atmospheric densities along CHAMP and GRACE-A orbits, and the density errors were calculated based on the high-accuracy accelerometer densities, empirical models errors including NRLMSISE-00, JB2008 and MSIS2.0 were also estimated for comparison. Improvement ratios, which defined as the percentage of TLE density errors smaller than that of empirical models, were given in the subsequent contents, and lay a theoretical foundation for the accuracy and application of the TLE-derived densities. TLE data ranged from 2002 to 2017, and two different kinds of densities, including TLE-averaged and TLE-calibrated densities, were derived. The former ones have a temporal resolution of 3 days, and were independent of the empirical models; the latter ones were calibrated values which relies on the empirical models. Results indicate that the TLE-averaged densities have a general average error smaller than 5%, and a standard deviation no bigger than 8%; the TLE-calibrated densities have the minimum errors during geomagnetic quiet conditions, with the improvement ratios bigger than 80%.