In the present paper, the theoretical expressions for the axial strain sensitivity of high-birefringence fiber loop mirror (Hi-Bi FLM) was developed. The key influence factors on the axial strain sensitivity are discussed for the same input light source as the high-birefringence fiber material is certain, including the high-birefringence fiber length and the sensing length. The relationship between the high-birefringence fiber material and the axial strain sensitivity is discussed for the same input light source. The results show that the wavelength shift of high-birefringence fiber loop mirror is linear with the axial strain, and the linear sensitivity is constant decided by the high-birefringence fiber material and the center wavelength of input light source, having nothing to do with the high-birefringence fiber length and the sensing length.