The observation monitoring and evaluating system in NMC/CMA is described. This system includes the function of data processing, data quality control, bias statistics and analysis, products releases etc. The complex quality control and advanced evaluation technique are adopted. As an operational system, some observation problems are found and have been improved. The products also were used in verification of the bias correction scheme for 59 radiosonde and in the quality analyses for L-band digital radiosonde. A great contribution was made by the system on the management of observation operational, the improvement of observation quality and the application of observation data.