The strength and deformation characteristics of the replacement material of rockfill after scaling differ from those of the original rockfill. Studying such difference is of vital scientific value. In this paper, the influence of scaling method and maximum grain size of specimen on the critical state and the critical state equation were examined by looking into the stress and deformation characteristics of replacement material via triaxial consolidated drained shear test. The similar gradation method and the mixed method were adopted for the scale reduction of weakly-weathered limestone, and the maximum grain sizes of the designed gradations were 60 mm, 40 mm, 20 mm, and 10 mm respectively. Results unveiled that under the condition of the same maximum particle size, the volume change of the sample with mixed scale was larger than that of the sample with similar grading scale, and the particle breakage forms of the samples with different scales were different in the shear process, while the critical state lines of the two groups of samples on the Q-P′ plane were nearly coincident. The degree of particle breakage was described by introducing fractal dimensions. The particle fractal dimension after shearing was in a power function with confining pressure and was also related with maximum particle size. In addition, the equation of critical state line in consideration of maximum particle size of particle breakage was established in e-lgp′ plane, and the determination method of each parameter was also given. The research finding provides an idea for further constructing the critical state constitutive model of rockfill in consideration of scale effect.