The invention relates to the field of biotechnology, and discloses a porous silicon biochip and a preparation method thereof. The porous silicon preparation method provided by the invention comprises the steps of adopting electrochemical anodic oxidation technology to corrode a single face polished silicon wafer to obtain the porous silicon, wherein the oxidation mode is constant current electrolysis, the current density is 3mA/cm2 and the electrolysis time is 500-700 seconds; then performing modified decoration for the surface of the porous silicon by a functional silane coupling agent to obtain a modified layer containing active groups; and then preparing the porous silicon biochip by the functional porous silicon as a carrier. The preparation method provided by the invention is simple and convenient, requires fewer devices and is suitable for volume-production. The porous silicon biochip obtained by the method of the invention has the advantages of high sensitivity, good selectivity, good repeatability and the like, and can be used to study the interaction among biological macromolecules.