In this paper,a label free,fast,convenient,low-cost and high-s ensitivity biological detection method is proposed.The method takes advantage o f the optical properties of porous silicon photonic devices,and directly measur ed the change of refractive index of samples by ellipsometry,a single-layer po r ous silicon sample is used as the sensor substrate,the echinococcosis (Egp38) a ntigen was linked to porous silicon,then different concentrations of Egp38anti body molecules were added to the samples,after specific reaction between antige n and antibody,the change of refractive index was measured by ellipsometry,stu died the relationship between the degree of biological reaction and the change o f refractive index in the sensor,then realized the biological detection.The de tection limit of hydatidosis is 142nM.