The invention discloses a room-temperature high-sensitivity silicon-substrate photoconduction terahertz detector and a preparation method thereof. The detector uses a Silicon On Insulator (SOI) chip as a substrate, and a Reactive Ion Etching (RIE) silicon detection microbridge is formed on the substrate. Two ends of the silicon detection microbridge are connected with gold film electrodes. The invention further discloses a method for preparing the detector. The detector is operated in the room temperature, has the characteristics of high sensitivity, rapid response time, and simple preparation, is convenient for manufacturing a large-scale array chip, and has the extensive application prospect in aspects, such as the terahertz material detection and the terahertz imaging.