To investigate influence of birefringence on axial strain sensitivity of birefringence fiber loop mirror, change of axial strain sensitivity with birefringence is drawn by numerical simulation for the same strain dependent birefringence coefficient and different birefringences fibers. The simulation result shows that the axial sensitivity reduces with the increase of birefringence. The axial strain sensitivities of different birefringence fiber loop mirrors are compared by experiment. The curve of birefringence versus the axial strain sensitivity is fitted. The experimental fitting curve is in agreement with the simulation one. The result shows that the axial strain sensitivity can be improved by choosing a low birefringence fiber, but the birefringence can not be too low to measure axial strain because of generating weak interference spectrum.