It designed a simple system device which can detect the concentration of melamine in pure milk in this paper. Using the visible-near infrared light source to irradiate melamine-contained milk solution, the reflection spectra would have obvious change at the wavelength of 500 nm with the increasing concentration of melamine in pure milk, and the reflection spectra are nearly overlapped at the wavelength of 1000 nm. Based on this principle, combined with the photoelectric technology and computer technology, collecting light at 500nm is used to determine the concentration of melamine, and collecting light at 1000nm is used to eliminate the Interference of other ingredients in milk. The experimental result shows that, when the concentration of melamine is not less than 3 , the relative error produced by the device is less than 1%. And the device can quickly detect whether the milk containing melamine in real-time and accurately show the concentration of melamine, which make the device have strong practicability.