Abstract: In spite of the fact that the first patent on transient operation of chemical reactor was applied in 1938,the forced unsteady state operation of chemical reactors as an attractive novel technology and its associated profound theory are a new area of study in chemical reaction engineering.This paper briefly reviews its research history,the present situation and perspectives.Basic scientific questions and important experimental technics used and relevant to this area are primarily discussed.Some suggestions are made to promote more systematic and deeper studies on the unsteady state catalysis and forced period operation of chemical reaction systems with different scales.