An on-line automatic analyzer system for an interfacial polymerization polycarbonate polycondensation reactor has been developed. This analyzer system has two analyzer units, which are respectively set up for two sections in polycarbonate plant, and moreover the analyzer controlling system atilizes DCS (Distributed Control System). One analyzer unit is applied for checking oligomer in the first polycondensation reactor and the other is applied for measuring the unreacted raw material in the second polycondensation reactor. These analyzer units take advantage of titrators, and these units include hydrolysis of oligomer, washing of the beaker and, electrode sensor, and are operated by fully automatically. Accuracy of the data obtained by the on-line automatic analyzers is equivalent to that of the conventional manual operation. The measured data are calculated by DCS to make the analyzer controlling system manipulate raw material control valves. This system contributes to the stability of quality control, operation, labor saving and improvement of safety of the plant.