The invention relates to a brake drum, in particular to a vermicular iron brake drum and a preparation method thereof. The vermicular iron brake drum comprises, by weight, 3.3-3.6% of carbon, 2.2-2.65% of silicon, 0.45-0.6% of manganese, 0.2-0.3% of copper, 0.2-0.3% of chromium, 0.2-0.3% of zirconium, 0.2-0.3% of niobium, 0.06-0.09% of titanium, 0.025%-0.04% of rare earth, no more than 0.07% of phosphorus, no more than 0.035% of sulfur, no more than 0.035% of magnesium, and the balance iron and inevitable impurities. According to the mechanical properties of the vermicular iron brake drum, the tensile strength is 430-450 MPa, the elongation is 3.0-3.8%, and the hardness is 280-300 HB; and the vermicular iron brake drum has good heat conductivity, high-temperature strength, high-temperature abrasion resistance and heat fatigue resistance and is particularly suitable for heavy-duty automobiles, braking safety is greatly improved, and the service life is greatly prolonged.