A method of coating a polymeric resinous thin film on the surface of a tubular braid reinforcing material, wherein a polymeric resinous coating material is spin coated on the surface of an annular braid, the coated braid is extruded into the air, and the coating material is coagulated in a coagulating bath, wherein the ratio of the spin coating feed ratio (Q) one the braid advancing speed (v) with respect to a unit outer diameter (D.sub.0) of the braid is represented by the formula.function..times..times..function..times..times..function..times..- times..times..function. ##EQU00001## within the range of 200 to 3,000 g/m.sup.2.