The invention relates to a method for preparing an RPC (Reactive Powder Concrete) trench cover plate of a high-speed railway passenger-dedicated line. The method is characterized by comprising the following steps of: (1) preparing a mould; (2) preparing slurry, wherein the slurry comprises the following raw materials in parts by weight: 100 parts of silicate cement, 10 parts of siliceous dust, 110 parts of quartz sands, 10 parts of active mineral admixture, 35 parts of quartz powder, 2.5 parts of water reducing agent, 28 to 31 parts of water, and 0.2 part of polypropylene fibers, the silicate cement, the siliceous dust, the quartz sands, the active mineral admixture, the quartz powder and the polypropylene are stirred in a stirrer, the water reducing agent is dissolved with water, and the water reducing agent is added into the stirrer and the residual water is stirred in the stirrer to obtain the slurry; (3) shaking and molding; (4) initially setting; (5) demolding; and (6) maintaining to obtain the RPC trench cover plate of the high-speed railway passenger-dedicated line. By the method, the mechanical performance of the RPC trench cover plate can be improved, the anti-cracking and seepage-proofing performance and duration performance of the RPC trench cover plate can be reinforced, the production cost of the RPC trench cover plate can be reduced, and the preparation process is simple.