Wavelength dependency of polarization dependent loss (PDL) in reflection in uniform fiber Bragg gratings (FBG) written in single-mode fibers (SMF) is studied deteriledly. Effective PDL (PDLeff) and simulations are carried out using the coupled-mode theory and the Jones matrix. The evolution with wavelength of PDLeff as a function of the grating parameters and the birefringence value is analyzed. The PDLeff appears clearly on the band edges of the reflection spectrum, especially with the steep sides. Numerical results demonstrate that the PDLeff evolutions with wavelength can be strongly enhanced by a modification of the grating parameters. With increase of grating length and modulation depth, the PDLeff rapidly increases. For a given grating length and modulation depth of the grating, when grating birefringence is less than 2×10-5, the PDLeff increases rapidly with the increase of birefringence. As birefringence is greater than 2.5×10-4, the two main peaks with sub-peaks on it of the PDLeff become greater. With birefringence continuing increasing, the distance between the two main peaks increases, and the sub-peaks on the main peaks become smaller. They are presented a complete characterization of PDLeff in FBG and a good agreement between theory and experiment is got.