A non-reacting system and a reacting system are run with an on-line slit rheometer developed by the authors. It is found that the polyurethane-urea system behaves slightly elastic and the Zaremba-Fromm-Dewitt model may be employed to describe its rheological behaviors. After the gel time, the inside pressure of the testing materials varies dramatically. Reports in this respect have not been found in literature, as yet its mechanism warrants further studies.