The invention relates to a method for increasing the content of grease in primary sludge. The method comprises the following steps: stirring sewage; settling the sludge; according to different settling rates of sludge with different grease contents under a heating condition, separating a part with high grease content; selecting the sludge with a high settling rate as a raw material and performing hot drying to obtain dry sludge; grinding the sludge; extracting by a Soxhlet extraction method; evaporating extracting agents, heating substances subjected to grease extracting and drying after the extracting agents are completely evaporated to form a solid grease extract; performing methyl esterification on the grease extract, adding sulfuric acid and methanol solution into the solid grease extract to perform methyl esterification reaction, and then collecting extract products to obtain biodiesel. The method is simple and safe in operation and good in extraction effect and solves the technical problem of too low content of grease in the primary sludge.