The amyloid cascade hypothesis is the core of etiology of Alzheimer’s disease (AD). However, in the past few years, immunotherapy targeting amyloid plaques has not been successful. In recent years, different forms of amyloid β peptides (Aβ) have attracted people’s attention. Here, we summarized the research progress of different Aβ mutants in the brains of early-onset AD patients and the truncated and modified Aβ isoforms that have been identified in the brains of sporadic AD patients, particularly focusing on the aggregation characteristics of these Aβ species and their impact on the process of AD. Single amino acid Aβ mutations associated with FAD (familiar AD) lead to alterations in the structure of Aβ, which are associated with differential aggregation kinetics, morphologies, and conformations. These differences may underlie the pathological polymorphism of FAD. Meanwhile, enzyme digestion and post-transnational modification of Aβ may contribute to sporadic AD. Targeting these peptides or related enzymes can be used as a new therapeutic mechanism or provide a new diagnostic method. The currently reported detection and analysis methods of Aβ species was also summarized, including traditional mass spectrometry, immunoassay methods, and electrochemistry methods. This review may contribute to the in-depth study of the role of different forms of Aβ and related molecules in the pathological process of AD, and provide insight for the development of new methods for the diagnosis and treatment of AD.