The present invention belongs to technical field of medicine, and relates to the preparing of cleavable polyethylene glycol (PEG) lipid derivative and an application thereof in the liquid particle preparation. The general formula is as follows: CH3O(CH2CH2O)n-R-O-R, n=5-5000. The molecular weight of PEG is 300-30000. R represents one group selected from hemisuccinate group and carbomethoxy. The liposoluble fragment represented by R comprises one component selected from cholesterol, sitosterol, alpha-tocopherol. According to the invention, polyethylene glycol are connected with lipoid derivatives such as cholesterol, alpha-tocopherol, etc. through ester linkage. The cleavable PEG lipid derivative can be applied to the modification of liquid particle preparation. On one hand, the PEG lipid derivative has appropriate adhesive force of the surface of liquid particle preparation and guarantees enough holding time of PEG lipid derivative in blood. On the other hand, the PEG lipid derivative can gradually break away from the surface of preparation in the circulation process. The particle preparation which only comprises a few polyethylene glycol on the surface can combine and phagocytose the pathological cell. The medicine is delivered into the cell and therefore has the function of selectively killing the pathological cell.