Abstract: In this paper,the statistical reconstruction algorithms for PET and SPECT are discussed,including the history,the new improvements and the future.Three concepts that have significant meanings in the development of statistical reconstruction are summarized: Ordered Subset(OS),Incremental Method and Optimization Transfer(OT).In order to show the outline of statistical reconstruction in the past years,this paper focuses on the algorithms that have significant innovations in both concept and method,and introduces the main ideas and motivations of these algorithms.