The invention provides a method for detecting cecropin B based on a liquid crystal biosensor. The method is characterized in that N,N-dimethyl-N-octadecyl (3-[trimethoxysilyl] propyl) ammonium chloride/triethanolamine (DMOAP/TEA) is mixed on the surface of a self-assembled modified glass slide, and the liquid crystal molecule orientation is induced; the cecropin B is fixed on the surface of a self-assembled film-modified substrate by adopting an aldehyde group in the TEA; after a cecropin B antibody is specifically combined with the cecropin B on the surface of the glass slide, the liquid crystal molecule orientation can be disturbed, so that the change in the color and the brightness of an optical signal is caused. Therefore, the detection on the cecropin B is realized. The method provided by the invention has the benefit that when the cecropin B is detected, the advantages of the liquid crystal biosensor are combined, so that the method has the characteristics of being high in sensitivity, good in specificity, unmarked, simple to operate and the like.