The invention discloses a floor heating system heating pipe with a low linear expansion coefficient and a preparation method thereof. The heating pipe is prepared by performing matrix resin drying, feeding, blending, four-section single screw extrusion forming, argon vacuum sizing, water tank cooling, compressed air purging, traction, cut-to-length cutting, and coiling and crosslinking on matrix resin and an auxiliary agent with the mass ratio being 100: (0.76-1.08), wherein the matrix resin adopts HDPE, LDPE and PPR; the auxiliary agent adopts vinyl trimethoxy silane, dicumyl peroxide, dibutyltin dilaurate and an antioxidant. The heating pipe has the advantages that three types of matrix resin is adopted to be blended to obtain the best performance matching, and the adding of a small amount of auxiliary agent restrains the excessive crosslinking of pipes; through the adoption of a four-section single screw extruder with a large ratio of length to diameter, the grafting reaction efficiency is improved, and through the controlling of temperature, humidity and time, hydrolizing and crosslinking is more sufficient. The pipe has high tenacity and plasticity, and low expansion coefficient, is convenient for construction, and can be widely applied to the floor radiation heating field.