Abstract: The cell nucleus as the controller of all genetic and physiological activities within the cell,is the most prominent marker of eukaryotic cells.The formation of the cell nucleus is the key event during the origin of eukaryotic cells.The first appearance of the primitive cell nucleus indicates the emergence of the first eukaryotic cell.The research on the origin of the cell nucleus not only enriches the modern cell biology and evolutionary biology,but might also even influence the further development of the molecular cell biology by stimulating cell biologists to consider the significance of the viewpoint of evolution to cell researches.However,for a long time,on the origin of the cell nucleus there were only several reckless and assumptions and a few earnest efforts which were unsuccessful or only indirectly related to the formation of the nucleus.One of the main reasons for this situation seems to be the lack of a practical way for the study.Through searching for a long time we found a way.The essential point of the way is to consider the comprehension of the primitive nucleus as the key link for understanding the whole process of and early evolution of the cell nucleus.We have already known that the prokaryotic ancestor of eukaryotes must be one kind of ancient archaea (Li,1999).The primitive cell nucleus should be an intermediate link between the archaeal nucleoid and the typical cell nucleus.In order to obtain some features of the original nucleus,We d better study the most primitive protists we can find today and investigate all aspects of their cell nucleus thoroughly.Then,combined with the present knowledge on archaea we would be able to propose a hypothetical model for the primitive cell nucleus,and arrange various possible experiments to examine it from various aspects in order to test,to modify,to improve it,or replace it with a new one.Along this way,we would finally obtain a convincing model of the primitive cell nucleus.Then,combined the model with the present knowledge on archaea,protists and eukaryotic cells we could establish an all-sided hypothesis on the origin and early evolution of the cell nucleus for further examinations.Further along this way we would closer and closer approach the real evolutionary process.This is a realistic way.Along this way we have already negated the dinoflagellate nucleus model and the related hypothesis and established the diplomonad nucleus model for the primitive cell nucleus and proposed a rather complete theory on the origin and early revolution of the cell nucleus,including the origins of nuclear envelope,eukaryotic chromosomes and nucleolus (Li,1999).