To effectively reduce the specific fuel consumption of aeroengine and obtain the optimal geometric design parameters of compliant cylindrical intershaft gas film seal(CCIGFS) in the limited design space size, an optimal design method of CCIGFS based on the grasshopper swarm characteristics is established, and the optimal design parameters of CCIGFS for counter-rotating shafts are acquired by this method. In this paper, for the sake of leakage calculation, mechanical characteristics of the seal are analyzed and a fluid-structure coupling model of CCIGFS for counter-rotating shafts is built. This fluid-structure coupling model considers the influences of centrifugal expansion and rotor circular precession. Then, according to this method, the leakage rate with various seal widths and diameters is computed and the function relation of leakage rate with seal width and diameter is obtained by curve fitting method. Furthermore, by changing the design parameters of the seal width and diameter, the functional relation between the mass and the seal width and diameter is obtained by curve fitting method too. Thus, the multi-objective optimization design model about the design variables of the CCIGFS is developed. Finally, the state-of-the-art multi-objective grasshopper optimization algorithm is adopted to obtain the corresponding Pareto frontier, and the geometric structure design parameters of the seal are selected according to the actual situation. This paper provides a complete and systematic method for the engineering design and analysis of CCIGFS in the counter-rotating shafts.