Abstract: The operation monitoring system aims to monitor L band upper air meteorological sounding network running conditions including instrument running status and sounding data quality. Based on B/S structure, Windows platform and Oracle database, it can ensure users visit the monitoring system website at anytime and anyplace. The surface radar running condition monitoring file will be automatically generated 5 minutes after balloon releasing, and upper air sounding data monitoring file that contains upper air sounding statistics results and upper air sounding minutely data will be generated when upper air sounding process finishes. The TTAA message arrival information is used to judge whether L band upper air sounding system is working, the surface radar running condition monitoring file i s used to judge whether the surface radar working status is normal, the TTAA mes sage and upper air minutely data are used to check data quality. The monitoring system is developed fully considering monitoring information and sounding data provided by upper air meteorological sounding system, integrated operational running experience and users' requirements. The sounding parameter, surface instan taneous observation data and surface radar running status parameters can be displayed and checked, and sounding result can also be displayed and analyzed by th e system. During the sounding data quality control, first the message format is checked, and then based on WMO's reference criteria for AWS instantaneous extreme value check the surface instantaneous extreme value check is carried out. The nationwide monitoring area is divided into northeast, northwest, middle and south subareas. The geopotential height and temperature thresholds of each subarea are set using compiled upper air sounding data of CMA. Spherical coordinate data including elevation, azimuth, slant range and height are added to the monitoring file, and they are used to check the consistency of upper air sounding data and quality of the wind data. The sounding data quality check diagnoses the facility problems automatically and can improve its performance. The results show that the surface radar and radiosonde problems and current running status can be found immediately through the monitoring system integrated with sounding data quality check. The system can guarantee the operational stability of upper air mete orological sounding network, and improve meteorological sounding data quality effectively. But during the sounding data quality assessment the thresholds are found to be too strict, so it should be modified to avoid too much false warning information through further running assessment.