Long period fiber gratings (LPFGs) can sense changes in the environmental medium through the coupling between core fundamental modes and cladding modes, thereby achieving perception of the external environment. They have many advantages such as high sensitivity, small size, low back reflection, and resistance to electromagnetic interference, etc., and have been applied in various fields such as food safety, environmental detection, disease diagnosis, and so on. In this paper, the progress of the application of LPFGs in biological detection technology in recent years is summarized. Firstly, the principle of LPFGs for biological detection is elucidated. Secondly, the common fixing methods of the biological functional films on the surface of LPFGs are introduced, and then the applications of LPFGs in the detection of biological substances such as DNA, glucose, bacteria, cancer, and viruses are summarized. Finally, the challenges faced by LPFGs in biological detection technology are analyzed, and the future development of LPFGs in biological detection technology is prospected.