Replacement  of  the  elderly  group  has  gradually  become  a  normal  phenomenon  of  population ageing  in  China． However ，current researches still focus on the size and structure of population of the elderly people． Thus ，it is of high importance to give an account of the replacement of the elderly group and to construct  a corollary  group analysis． This research proposes a theoretical framework for the group analysis including  concepts ，theories ，propositions ，indexes ，and applications．  The elderly group in this research refers to a cohort  group  having  same  experiences ，which  is  a  demography concept． Differences  within  the  elderly group ，which  can be explained by the life － course theory ，dynamism theory and chaos theory ，can be attributed to the effects of the environment and social construction． The differences can be measured by the indexes involving background ，capability ( behavior  and  consciousness) ，and  need． Paying  special  attention  to the group replacement ，caring about its initiatives ，dialectically analyzing its influence and adding a perspective of  group replacement to policies are among the important  areas of  applications of  the research

Identity is an important aspect of mental health of the disabled elderly.Based on the data of in-depth interview with disabled elderly in Beijing,this research examines the main contents,characteristics and strategies of the identity problems associated with the disabled elderly from demographic and sociological perspective.We have found that their identity involves in four aspects: individual identity,personal identity,group identity and social identity,which all have profound effects on their daily life and the quality of life.We suggest that alleviating their sense of "inferiority",strenghtening their recognition of group identity,and optimizating the recognition of "socialized people" are important approaches to improve the mental and psychological status,and to promote the quality of life of the disabled elderly.