The invention relates to a preparation method and an application of an effective part of dracocephalum heterophyllum benth. The method comprises the steps that an aboveground part of the dracocephalum heterophyllum benth is smashed, extracted by an organic solvent, namely alcohol, and subjected to macroporous resin separation and purification to form the effective part of the dracocephalum heterophyllum benth. A preliminary activity screening test proves that the effective part of the dracocephalum heterophyllum benth obtained by the method has functions of lowering renal hypertension and rat blood pressure, and enhancing diastole and systole, and can also effectively prevent and treat hypertension complications including myocardial hypertrophy, renal injuries and vascular endothelial injuries. The method is simple in technology, low in production cost, and easy to control, and does not require high temperature or high pressure equipment, and the quality of the effective component is stable.