By means of the radiosonde data and retrieved data during some important activities in Beijing, evaluation and analysis are conducted from the aspects of the errors of the total average, the differences at different times, and weather conditions with or without rainfall. The results show that (1) Total average: the error variation range of temperature was great in rainy days, and small in no rain days. The retrieved temperature from microwave radiometers was closer to the radiosonde temperature in rainy days than in no rain days. The error variation trend of relative humidity was similar to that of temperature, but for the relative error, the values in rainy days were smaller than those in no rain days. (2) Different times: the statistic parameters of temperature varied with height, and the regularity was obvious in no rain days, but not in rainy days. In no rain days, the error was the smallest at 20:00, closer to the radiosonde measurements and the greatest at 14:00. In rainy days, the errors at various times were bigger than those in no rain days, and the retrieved temperature from the microwave radiometer data at 20:00 was close to the radiosonde measurements. For relative humidity, the regularities were obvious and the variation trend was the same as in no rain days, but not in rainy days. Generally, the influence of rainfall on the retrieved data from microwave radiometers is greater. The error of the retrieved data was the smallest at 20:00. The statistic value varied most obviously at 5000 m, relative to clouds.