The invention discloses low temperature fermenting Lactobacillus casei and a method for preparing hard yark milk cheese from Lactobacillus casei. The Lactobacillus casei which has a preservation number of CGMCC4775 has a low temperature fermentation capability. The method for preparing the hard yark milk cheese from Lactobacillus casei comprises steps of raw milk sterilization, inoculation, fermentation, enzyme addition, milk curding, cutting, whey discharging, pile brewing, squeeze-molding, packaging, and maturation. The hard yark milk cheese, which is prepared in the invention, is milky in color and has the characteristics of rich milk fragrance, uniform quality and abundant nutrition, has the advantages of good hardness, good elasticity, good cohesiveness and good chewiness.