Sampled grating DBR (SGDBR) lasers are the most promising one of the tunable lasers applied in optical communications.The spectral characteristics of sampled grating DBR semiconduct" or lasers was modeled using transfer matrix method.Gain region, phase region and sampled grating DBR are regarded as elementary parts in calculation.Every elementary part is regarded as a two"port device whose transmission property is expressed by a 2×2 complex matrix.Below threshold, emission spectra show different output characteristics under different injection currents into gain region and SGDBR.When the current injected in the active region is 9.5 mA,a main mode begins to arise near 1.553 μm. When there are currents in a sampled grating DBR, the positions at which main modesbegin to arise vary,which shows tunability.Meanwhile the current injected in the active region also varieswhen a main mode begins to arise.Threshold condition is also reflected using this method.Threshold currentis 10 mA.