The comparative analysis on observation data of the L band radar sounding system and 59 701 sounding system by four sounding stations in Sichuan is made in this paper. The results indicate that temperature and geopotential height data observed by 59 701 sounding system made in Taiyuan are higher than that observed by 59 701 sounding system made in Shanghai. The temperature and geopotential height data below 100 hPa do not change obviously after using L band sounding system, but above 100 hPa they change obviously. Humidity data measured by the two sounding systems have large differences. The differences near surface are small, increasing with height. Most of the humidity data measured by L band sounding system are lower than that measured by 59 701 sounding system. The differences between average wind direction and velocity measured by the two sounding systems are small. Peak value differences of all elements are large. The discrete case of each elements difference changes with different heights. The greatest degree of general discrete is geopotential height, secondly is the wind direction, humidity, dew point, wind speed, and temperature in sequence. The trends of differences between the two sounding systems are not large, but relations exist between the difference changes of humidity, wind direction, wind speed and the geographic location, season, and releasing time. There are differences between L band and 59 701 sounding systems in equipment, measuring principle, measurement accuracy, the revised statistics, methods of observation, releasing time and so on.