According to the market demands of developing low-cost optical fiber pressure and flow meters, an effective method of integrating a limited number of ordinary narrow-band light sources into a small wide-band light source is proposed. Research results show that multiple narrow-band light sources with different wavelengths, which meet certain conditions, can be changed into a small broadband light source by coupling multiple optical fiber couplers. By adjusting the internal current of the narrow-band light source and changing the output light intensity, the spectral flatness of the small-scale broadband light source can be effectively improved. With the help of mathematical algorithm, the judgment basis for the optimal spectral quality of the small broadband light source is proposed theoretically. By using the spline fitting function, the program can be written, and the output light intensity of a single light source can be automatically adjusted by controlling the current effectively. Research results show that the small broadband light source developed by this new technology has the characteristics of low manufacturing cost, small volume, high spectral flatness and adjustable intensity, and the spectral width can reach 2~3 nm. The simulation testing shows that the proposed method is effective.