A simulation model of the fiber DBR (distributed Bragg reflector) laser with two sampled Bragg gratings (SBGs) as reflectors is established, with which the characteristics of the laser are analyzed in detail. The analysis mainly focuses on the change of the laser output characteristics with the wavelength and reflectivity of the front and back sampled fiber gratings. Because of the multi-channel reflection of SBGs, the side mode of such laser is always very obvious. The method for improving the SMSR(side mode suppression ratio) is suggested. And the wavelength tuning mechanism is also studied. Experiment has been carried out to confirm the analysis.