Abstract: As a high performance indicator of complexometric titration and luminosity chromogenic agent with more than 200 products, pyridylazo reagents are widely used for spectrophotometric analysis of various kinds of metal ions. In order to improve the performance of analysis, further researchs was undertaken to study the correlation of the structures and function of pyridylazo reagents, and a series of high performance pyridylazo reagents were produced. A review of pyridylazo reagents in the spectrophotometric analysis of metal ions from 1990 to 2010 is introduced in this paper. The application of pyridylazo reagents in the real samples is presented from different aspects such as reaction system, maximum absorption, sensitivity, linearity range, etc.