Different sunlight spectrua make different regulation on the photosynthesis and physiology of plants. The detection of different bands light intensity is the foundation of the highly efficient supplementary lighting. Because the existing specific band intensity detection instruments have the disadvantages of high cost and easy to expand, a new method of rapid detection of specific waveband intensity was presented. Taking red and blue as an example, the percentage of specific waveband accounting for sunlight was obtained. By using Matlab, the least squares method was adpoted for fitting function, combining with the calculation formula of sun elevation angle, and a multiparameter coupling model between the percentage of specific waveband accounting for sunlight and the date, time, latitude and longitude was established. The specific waveband intensity was rapidly calculated by realtime detecting the intensity of sunlight. Experimental results showed that measurement error of the method is less than 4.5%, which can satisfy the need of light intensity detection of the subband of light filling system.