The most important factor is a design of accurate real-time quality estimator for successful APC(Advanced Process Control) project. This research deals with design of real-time quality estimator for TSC (Total Solid Content) that is one of the most important specification of polymer products. In the general distillation process, temperature or pressure at the internal parts of tower where are interested positions are usually chosen as key measurement variable. In the polymer stripping process, however, flow rate recycled into bottom of tower is more appropriate. It is important to choose what is proper measurement variable depended on what specification must be estimated or what ingredient is dealt with at the process.