A system for monitoring a mean value and a standard deviation in an on-line way comprises an original data acquisition device, a data grouping processing unit, a plotting processing unit and a front end displayer all connected in sequence. The system adopts a central limit theorem, the statistical inference and a box plot tool to realize that the content which needs to be monitored by a traditional Xbar-S/Xbar-R control chart on two charts can be monitored by the system on one chart, and make up for the defect that a pre-control chart cannot monitor wave (S or R). As the box plot not only can identify an abnormal value quickly, but also can enable an IQR (Inter Quartile Range) of the box plot to be less affected or not to be affected by the abnormal value, the box plot is more suitable for the quality control of tobacco production at the aspect of identifying the abnormal value and expressing the procedure wave. In addition, the system has the advantage that a confidence coefficient combination can be configured flexibly to meet the requirements of different control stringencies. The traditional control chart is not endowed with the advantage.