Based on the principle of the differentiating interferometer,a novel optical fiber sound sensor was presented. The theory was analyzed and the mathematical model was given. The expression of the output signal was obtained and analyzed. A wideband sound signal source was studied in experiments. The experimental results accord with the theory analysis,The interferometer not only resolves the narrow linear range of conventional bibeam interferometer, but also simplifies the signal processing circuitry. The light source with short coherent length can be used. The inaccuracy of the location of the wideband sound signal source is less than 1% and the result is out of the effect of slow circumstance variables.