A Fabry-Perot (F-P) semiconductor laser (FP-LD) was single mode injection locked by a distributed feedback semiconductor laser (DFB-LD). The characteristics of optical spectrum, output power and frequency response were investigated by adjusting the bias current of the FP-LD, the output of the DFB-LD and the wavelength detuning between the master and the slave laser. The factors that affect the stability of injection locked FP-LD were analyzed. The stable range of injection locking was given. By optimizing the injection conditions, the side mode suppress ratio (SMSR) of the injection locked FP-LD as high as 55 dB was demonstrated. Comparing with the free running FP-LD, the injection locking technique can suppress the spread of the spectrum under high speed modulation. The 3 dB tuning bandwidth of 14 GHz was achieved. The results indicate that with injection locking the characteristic of optical spectrum and frequency response can be improved, by which the FP-LD can apply to the high speed fiber communication system.