In order to make the results of teeth color measurement in the field of dental cosmetic more accurate, this paper has designed a color monitoring instrument, which is based on the colorimetry principle. It used the white-balance adjustment method, technology of integrated digital circuit and design of handheld structure. The source of the instrument was LED light. The core was a mega128 microcontroller. TCS230 programmable color sensor was used to gather the color signal, and C language was used to realize the collection, the storage and the display of the color data. In the experiment of comparison of the measured color with the international standard color card, we analyzed several factors, which affected the accuracy of the measurement. The instrument had a series of advantages, such as high measuring accuracy, high stability, low-power consumption and easy to carry. In short, the instrument has promising applications and broad market.