In "Second Meditation" Descartes proved that "I exist" and "My essence is the thing of thinking", and then equated "I exist" with "My essence", forming the famous proposition "I think, therefore I am." The relationship between "I think" and "I am", and the specific connotation of "I think, therefore I am" can be clarified through sorting out the argument structure in "Second Meditation". Through the analysis of the self-relationship in this proposition, "I think, therefore I am" can be reconstructed into a more logical "I think I am, therefore I am." On this basis, the two "I"is in the premise need to be regarded as the same subject, and the scope of their reference should be limited to pure thinking.