Abnormal tooth color is the most important factor affecting the aesthetics of teeth, exogenous coloring and endogenous coloring are the two major causes of tooth discoloration, tooth bleaching is an effective method for treating tooth discoloration, which can be divided into: 1. Internal bleaching: mainly applied to dead pulp teeth 2. External bleaching: further divided into: (1) home bleaching: home bleaching has undergone the development process from in medicine trays, bleaching coating to dental paste; (2) clinical Bleaching: Laser bleaching and cold light bleaching are the two most common clinical bleaching methods. The exact mechanism of tooth bleaching is not very clear, and it is generally believed that bleaching is accomplished by the oxidation reaction of hydrogen peroxide. Tooth sensitivity is one of the most common side effects of tooth bleaching process, which is generally manifested as hypersensitivity to cold and hot stimuli and can appear early in the bleaching process, and usually disappears 24-48h after the termination of bleaching. Factors affecting the efficacy of bleaching treatment include: pH of the tooth surface or even in the mouth, the effect of light, age factor, concentration of bleaching agent, staining site, degree and staining pattern, and bleaching time. The use of scientific methods to evaluate the color change of teeth before and after bleaching is the key to evaluate the efficacy of bleaching treatment. The visual colorimetric method, the instrumental measurement method and the computer-aided analysis method are the common methods to evaluate the color change of teeth before and after bleaching, among which the computer-aided analysis method is the most objective and accurate method to evaluate the efficacy of dental bleaching. According to our research results, bleaching treatment is currently a proven treatment for discolored teeth.