Novel quantum-dot optical amplifiers obtain development and applications, because they possess the advantages of broader bandwidth, higher gain, lower noise and higher power amplification. Starting from the structure and main characteristics of quantum dots, this paper summarizes the research and application status of several common quantum dots in optical amplifiers. Whereafter, the basic structure and working mechanisms are emphatically introduced for the quantum-dot semiconductor optical amplifiers and fiber amplifiers. The spectral characteristics of CdSe/ZnS quantum-dot optical fiber are briefly described. Some problems awaiting solution to further developing quantum-dot optical amplifiers are proposed and an outlook is given for quantum-dots applications in optical communication field.