After taking into account the phase distribution of the Fiber Grating（FG） and starting from the threshold condition of the Fiber Grating External Cavity Semiconductor Laser（FGESL）

the influence of the front facet（facing the FG） reflectivity on the lasing wavelength variation of the Long-External-Cavity Fiber Grating Semiconductor Laser（LECFGSL） with the ambient temperature has been investigated theoretically.The numerical simulations show that

with the ambient temperature variation

the lasing wavelength of the LECFGSL will fluctuate around the FG Bragg reflection wavelength;the front facet reflectivity has an obvious influence on the fluctuation amplitude of the lasing wavelength

and when the front facet reflectivity is less than 10

-4

the lasing wavelength of the LECFGSL is nearly equal to the Bragg reflection wavelength of the FG.