The invention relates to a method for preparing 
grease rich in DHA and special equipment therefor. The method comprises the following steps: in an 
aeration fermentation tank containing a 
fermentation culture medium, cultivating 
schizochytrium CGMCCNo.7693 in a mechanical stirring manner; and extracting and recovering the 
grease rich in DHA from 
schizochytrium cells, wherein the culture process comprises continuous fed-batch cultivation of a medium, 
sedimentation-adverse 
perfusion of cells, and periodical 
discharge of 
fermentation liquor; the special 
cell sedimentation tank comprises a primary 
sedimentation tank, a secondary sedimentation tank, seal covers, openings and outlets; the primary sedimentation tank and the secondary sedimentation tank are arranged at an interval and are of conical shapes in appearance; the seal covers are arranged on the primary sedimentation tank and the secondary sedimentation tank; the openings are formed in the seal covers; the outlets are formed in the bottoms of the primary sedimentation tank and the secondary sedimentation tank; a liquid inlet 
pipe is arranged on the primary sedimentation tank; a supernate 
discharge pipe is arranged at the upper part of the secondary sedimentation tank; the primary sedimentation tank and the secondary sedimentation tank are connected through a communicating 
pipe; and the outlets are connected with a fermentation tank through concentrated 
cell reflux pumps and pipes. According to the method and the special 
cell sedimentation tank, the problems in a micro 
algae continuous cultivation technique that cells are difficultly intercepted and 
cell loss is serious are solved, the special cell sedimentation tank has the advantages of reduction of manual operation, easiness in automatic production, short 
production cycle and the like.