The invention discloses an isotropic polypropylene composition with low linear expansion coefficient and a preparation method thereof, and belongs to the field of modified plastics. The isotropic polypropylene composition with low linear expansion coefficient, provided by the invention, is prepared from the following components by mass percent: 20-98% of polypropylene, 2-20% of crystal whiskers, 0-30% of mineral powder, 0-20% of a flexibilizer, 0-5% of a compatilizer and 0-5% of other auxiliary agents, wherein the crystal whiskers adopt three-dimensional tetrapod-like structures and are isotropic, and the length-diameter ratio of each crystal whisker in single direction can reach 50 above. According to the polypropylene composition, the linear expansion coefficients of the polypropylene composition in the transverse and longitudinal directions can reach 4.0*10<-5> below by virtue of the added crystal whiskers, and the purpose of isotropy can be achieved. The polypropylene composition prepared through the method can be applied to inner and outer decorative parts of automobiles.