The optimal intensity noise suppression of a Fabry-Perot （FP） laser is experimentally acquired by relatively strong external optical injection locking technology. The maximum suppression is up to 9dB around the relaxation oscillation peak of the free running FP laser. We demonstrate how the injection light power and detuning frequency influence the intensity noise suppression effects. Additionally, the relationship between the optimal suppression range and the stable locking range is experimentally studied：both ranges enlarge as the injection light power increases, but the stable locking range permits larger detuning frequency at identical injection light power.
