COSMIC （Constellation Observation System for Meteorology， Ionosphere and Climate）， a spacebased GPS constellation observing system of six lowearthorbit satellites, provides approximately 2000 to 3000 profiles of atmospheric temperature, pressure, humidity from 40 km to the ground each day, and greatly enhances the atmospheric observation in spatial and temporal resolution. To evaluate the accuracy, the COSMIC observations were compared with the L band radiosonde from May 20 to November 26, 2008. The comparison of the wet profiles below 10 km showed that the deviation is -0.5 ℃ for temperature, 1.4N for refractivity index, 2.0 hPa for pressure, 0.1 hPa for vapor pressure; while their root mean square errors （RMS） are 1.5 ℃, 5.9N, 4.7 hPa, 1.1 hPa, respectively. As for the dry profiles, between 10 km and 30 km, the deviations are -0.3 ℃ in temperature, 0.4N in refractivity index, 1.4 hPa in vapor pressure, while the RMSs are 1.9 ℃, 0.9N and 2.6 hPa, respectively, which implies their potential applications in numerical weather prediction owing to the high spatial and temporal resolution and high accuracy.