Glacial lakes not only provide the important refresh water resources in alpine region, but also act as a trigger of many glacial hazards such as glacial lake outburst flood (GLOF)and debris flow. Hence glacial lakes play an important role in the research related with cryosphere, climate change and alpine hazards. In this paper, the issues of glacial lakes were systematically discussed. Then from the view of glacial lake inventory and glacial lake hazards study, the glacial lake was defined as natural water supplied mainly by modern glacier melting water or formed in glacier moraine's depression. Furthermore, a complete classification system of glacial lakes was proposed based on its formation mechanism, topographic feature and geographical position. Glacial lakes were classified into 6 classes and 8 subclasses, i.e., glacial erosion lake (including cirque lake, glacial valley lake and other glacial erosion lake), morainedammed lake (including end moraine-dammed lake, lateral moraine-dammed lake and moraine thaw lake), ice- blocked lake (including advancing glacier- blocked lake and other glacierblocked lake), supraglacial lake, subglacial lake and other glacial lakes. Meanwhile, some corresponding features presented by remote sensing images and quantitative indices for identifying different glacial lake types were proposed so as to build a universal and operational classification system of glacial lakes.