The invention relates to a biometric sensing system, comprising: a light emitter, a polarization sensor, and a signal processing module, wherein the polarization sensor includes a first polarizer and a second polarizer. First, the light emitter emits a plurality of emitted light from the object under sensing, and reflected by the object. Then, a first reflected light in a first polarization direction and a second reflected light in a second polarization direction in the reflected light are sensed by the polarization sensor. Finally, the signal processing module calculates a first reflectance and a second reflectance according to the first reflected light and the second reflected light, and generate a reflectance ratio based on the first reflectance and the second reflectance. As such, the user determines whether the surface of the object under sensing is 3D by the reflectance ratio, so as to achieve improving safety and saving costs.