The invention relates to the technical field of building coating, in particular to rubber for a medical rubber plug and a preparing method of the rubber. The rubber is prepared from, by weight, natural rubber, filler, white vaseline, stearic acid, accelerant, anti-aging agent, sulfur and microcrystalline wax. With accelerant DM, accelerant NS and polysulfide thiuram being accelerant for vulcanizing the rubber, and with the accelerant NS being an overspeed accelerant, the vulcanizing speed can be further increased; barium sulfate and lithium carbonate are added in the filler as raw materials for antibiosis and bacteriostasis, wherein barium sulfate is not dissolved in water and lipid, and the possible influence on the human body is avoided; in the production process, a vacuum die-casting machine presses the mixed rubber out, the speed of air exhaust in the rubber material is increased, the effect of air exhaust in the rubber material is improved, the press-out time is saved, and the quality of the rubber is also improved; by using the anti-aging agent AW, not only can the purpose of aging resisting be achieved, but also the use of the anti-ageing agent can be reduced to a certain extent, and the cost is saved.