The dynamics of semiconductor laser subject to optical feedback was studied analytically by the means of asymptotic analysis method. The stabilities of external cavity modes (ECMs) were analyzed, and the bifurcation boundaries of the ECMs were obtained. The stable regions of the ECMs are proposed and verified by numerically calculating the Poincare section of semiconductor laser carrier density. The bifurcation diagram of semiconductor laser carrier density at different effective injection currents was numerically calculated and the first Hopf bifurcation boundary was agrees with the first Hopf bifurcation boundary calculated by the asymptotic method under the low injection current conditions.