Abstract: Embryonic stem cells（ES cells）, that are derived from the inner cell mass（ICM）of early embryos at the blastocyst stage, have the ability of self-renewal and multiple differentiation capacity. Now ES cells have been extensively applied in basic research and clinical application. That ES cells maintain their undifferentiated state during culture is the prerequisite and basis of their application, and therefore it is necessary to elucidate the molecular mechanism. This review summarized the latest progress in the study on the molecular mechanism for maintaining the undifferentiated state of embryonic stem cells, and emphasized the function of differentiation suppression factors such as LIF, Oct-3/4 and Nanog.