Employing coupling mode theory, the reflection and transmission coefficients of uniform fiber Bragg gratings with the grating induced birefringence were given. Based on the coefficients, analytical expressions of polarization dependent loss in fiber gratings were then deduced according to its deterministic and nondeterministic measurement principles. The given expression can precisely determine the polarization dependent loss (PDL) of the uniform fiber Bragg grating written in the isotropic or low birefringence fiber, and can also numerically simulate the approximate PDL result of Bragg uniform fiber grating written in the high birefringence fiber. The derived result agrees well with the existed experimental curve.