Animal model is an indispensable way for diseases research,pathology mechanism investigate,clinic medicine therapy experiments.At present,HIV,HBV still damage human healthy seriously because there are no proper animal models infected by such human viruses to research procedure of diseases which are causes by HIV and HBV.If human stem cells,which grow and differentiate outside of human bodies,were engrafted into laboratory animals' bodies to form chimerism successfully,human would culture animal models AIDS and other serious diseases to do more deep research and make out appreciate therapy protocols. Now sheep,mice are chief laboratory animals for human stem cells engraftment,we will introduce the developmental status on human stem cells engraftment.