The invention belongs to the technical field of novel material manufacturing and application and particularly relates to a high-purity compact magnesium oxide target material and a preparation method thereof. Magnesium oxide powder subjected to planetary ball milling are further subjected to isostatic cool pressing and vacuum sintering to obtain the near-net formed high-purity compact magnesium oxide target material, wherein a vacuum sintering temperature is 1400-1550 DEG C, heat preservation time is 2-10h, and a vacuum degree is 0.1-1.0Pa. The high-purity compact magnesium oxide target material prepared according to the method is 98.36% or above in compactness, 100ppm or below in total impurity element content, 7micron or blow in average grain size, 3.0micron or below in size deviation and 0.4micron or below in surface roughness Ra. The magnesium oxide target material prepared according to the method is high in purity and compactness and fine and uniform in grain size. The preparation method has advantages of short production cycle, low production cost, high production efficiency and availability for batch production.