Abstract: Alzheimer's disease(AD)is syndrome which begins with memory loss and visuo-spatial problems.With an increase of elderly population in our country,incidence in AD will grow.Subsequently,a series of medical and social-economic problems are caused by it.Up to now,there is no effective treatment for AD.It is a good choice of making an early diagnosis of AD to take active intervention to improve survival.Pathology,etiology,current status of diagnosis of AD,advance and application of PET in diagnosis of early stage AD are included in this article.PET,which is a functional imaging tool,can be used to diagnose and identify early AD. With the development of new radio-tracers and improvement of quantitative analysis,PET will play a more and more important role in study on AD in the future。