The invention relates to a global concentration on-line observer for rectification process based on local concentration measurement and a method thereof. The on-line observer comprises concentration measurement devices connected with a rectification tower, a local concentration measurement point off-line selection analysis module connected with the concentration measurement device, a data storagedevice connected with the concentration measurement device and a global concentration on-line observer body connected with the data storage device, wherein the local concentration measurement point off-line selection analysis module comprises a concentration distribution description module used for generating analysis data, a sensitivity matrix analysis module used for selecting a first measurement point and a to-be-selected tower plate correlation analysis module for selecting other measurement points. According to the global concentration on-line observer and the method, the local concentration measuring points for the rectification tower are selected and analyzed, the concentration measurement devices are arranged at limited positions of the tower plates, so that the on-line observationof material concentration of all the tower plates is achieved, the quantity of the installed concentration measurement devices is greatly reduced on the premise of ensuring the global concentration observation accuracy, and the cost is saved.