Phytase is a type of orthophosphomonoester phosphohydrolase, which catalyticly initiates stepwise hydrolysis of phytic acid to release phosphate radicals and produce lower inositol phosphate derivatives. Phytase has great application potential in the areas of animal nutrition, resource conservation, environmental protection and public health. At present, the understanding in phytase diversity and classification is so confusing or even inaccurate that the research progress and level of phytase has been badly affected. In this paper, the phytase classification based on optimal pH and stereospecificity is briefly introduced first, and then the updated research advance in phytase classification based on structure and catalytic mechanisms and the attributes of the representative phytases are summarized and discussed comprehensively. It is of vital importance to take into consideration the classification standards especially to focus on structure and catalytic mechanisms when a given phytase could be fully and accurately understood and characterized.