The invention belongs to the technical field of aerogel preparation, and discloses a cheap and efficient preparation method of a hydrophobic silica aerogel. A silica gel is first prepared by using a sol-gel method, and then placed in a modified solution for modification treatment for 8-16 h, then solvent replacement is carried out by using anhydrous ethanol, and finally drying treatment is carriedout to obtain the hydrophobic silica aerogel, wherein the modified solution is a mixed solution composed of anhydrous ethanol, hydroxyl silicone oil, and an alkaline catalyst according to a molar ratio of 1:(0.02-0.1):(0.0005-0.0008), and the alkaline catalyst is triethylenetetramine, diethylenetriamine, ethylenediamine, tetraethylenepentamine or sodium hydroxide. The method uses the low molecular weight hydroxyl silicone oil as a hydrophobic agent to prepare the silica aerogel, the production cost of the aerogel is reduced, and a production cycle is shortened. The hydrophobic aerogel prepared by the method has the advantages of simple process, low cost, and relatively good hydrophobic effects.