The refractive coefficient and extinction coefficient of ferrofluids, and the reflectivity on the fiber-optic end face in ferrofluids versus external magnetic field intensity at different volume concentrations and temperatures were theoretically analyzed and numerically simulated. The results show that volume concentration and magnetic field intensity have a great impact on refractive coefficients and extinction coefficionts of ferrofluids. The sensing heads based on the reflection on the fiber-optic end face in ferrofluids were fabricated, and the optical measurement system was designed, so the relationship between reflectivity and magnetic field intensity was obtained. The experimental results agree with the theoretical analysis. By theory and experiment, the effect of extinction coefficient of ferrofluids on the reflectivity on the fiber-optic end face can not be neglected.