The invention relates to a building material railway transportation device adaptive to a rock heap side slope and a use method. The building material railway transportation device consists of three parts, i.e., a winch operation device, a feeding rail device and a feeding trolley; a controller in the winch operation device enables a motor and a gearbox to drive a winch roller to rotate at a certain speed, a traction rope is driven to move, and the traction rope drives the feeding trolley to move on the feeding rail device; the feeding rail device mainly comprises five parts, i.e., a rail, a sleeper, a sleeve, a supporting rod piece and a fixed pulley; hydraulic type telescopic legs are adopted as legs of the feeding trolley, and a reverse-preventing straight-moving wheel is adopted for each front leg. The building material railway transportation device can be used to overcome the defects of an existing rail device that the construction cost is high, the flatness requirement is high, building materials in a transporting trolley easily spill out, a traction rope is suddenly broken to make the trolley slip downwards, and the like, has the characteristics that detachment and operation are convenient, the construction cost is low, the practicability is high, the traction rope is prevented from being suddenly broken to make the trolley slip downwards, and the like, and is applicable to building material railway transportation on the rock heap side slope.