Combining near infrared spectroscopy technology with virtual instrument technology, a multi-band near infrared detector for grain component was developed. Adopted diffuse reflection principle, the instrument is composed of optical system, circuit system and software system. The working process is as the follows: being frequently modulated, the full spectrum light issued by halogen light was transformed into the scan spectra via the scanning spectral filter through the sample diffuse reflectance, then it was converted to electrical signals after being received by the detector. After that, a conditioning conversion was adopted, and finally it was sent to computer by the acquisition card for further processing. A system-testing was performed based on the 26 prepared samples. Test results showed that the equipment has low noise level, inferior reproducibility, and the forecast-accuracy is not very good. But the accuracy can be improved by way of measuring average after loading repeatedly. The instrument can be used for measuring many ingredients in the grain samples, such as protein, starch and fat.