A distributed optical fiber sensor system based on coherent Rayleigh backscattered theory is set up, and an optimized Erbium-doped fiber amplifier (EDFA) is designed. The influence of few key factors such as extinction ratio, sensing distance and reflections from the sensing fiber on backscattered profile are analyzed. Experiments show that: the peak power and extinction ratio of injection pulse can be obviously improved through properly adjusting the offset voltages of Electro-Optic Modulator and EDFA. Because of the limit of extinction ratio of pulse, the short distance sensing is easier to obtain good scattered waveforms than long distance sensing. Eliminating the Fresnel reflections from the front-end and back-end of the sensing fiber can also improve the quality and stability of the scattering signals.