Abstract: The modified carbonyl iron powders with single particle size (single-grading) and binary particle sizes (double-grading) were added in the composite gel, which was prepared by using methyl silicone oil, gelatin and agaropectin colloids as raw materials, and then the single- and double-grading magnetorheological composite gel (MRCG) was prepared by vacuum decompression. The effects of particle size and gradation of carbonyl iron powder on the rheological behaviors of the MRCG were studied. The results show that the shear strength of single-grading MRCG decreased gradually with the decrease of the carbonyl iron particle size. However, the shear strength of the double-grading MRCG with the gradation of 90wt% un-ball-milled and 10wt% ball-milled carbonyl iron powders first increased then decreased with the increase of milling time (the decrease of the carbonyl iron particle size) and reached 99.6 kPa after ball milling for 24 h, which was 17.8 kPa larger than that of un-ball-milled single-grading MRCG.