The invention discloses a liquid crystal polyester, a preparation method and a composition thereof as well as an application of the composition thereof. The liquid crystal polyester comprises repeated units: -O-Ar1-O- (II), -OC-Ar2-CO- (III) shown in (I), (II) and (III). The preparation method of the liquid crystal polyester disclosed by the invention comprises two steps of fusing prepolymerization and solid-phase polymerization. The difference between the crystallization temperature and the thermal deformation temperature of the obtained liquid crystal polyester is 10-20 DEG C, so that keeping of excellent processability of the liquid crystal polyester is facilitated when the operating temperature is kept. In addition, the liquid crystal polyester and the composition prepared from inorganic filler disclosed by the invention have excellent impact resistance and buckling deformation resistance, and can be widely applied to the field of electronic and electrical appliances.