Sheath flow is one of the key technologies for the optical detection of high concentration aerosol particles. Based on the aerodynamics theory and the related researches abroad, a gas sheath flow jet is designed to achieve the effective measurement of high concentration aerosol particles. First, a group of optimal design parameters are determined according to the simulation analysis by the Gambit and Fluent modules in the large-scale general finite element analysis software of ANSYS, and a real sheath flow jet is made as well. In addition, the simulation results show that the sheath flow jet can compress the diameter of sample air flow from 1 mm to 0.34 mm, and the compression effect is obvious. Then, a kind of experiment scheme is put forward, in which the compression effect of a sheath flow jet is indirectly analyzed using the size distribution errors of a particle counter. Finally, the comparison and analysis of 0.3 μm particle distributions are achieved for 1.0 mm ordinary jet, 0.5 mm ordinary jet and sheath flow jet on the same particle counter. The experimental results show that the sheath flow jet designed here can effectively reduce the overlap rate of dust particles and significantly increase the concentration detection limit of a particle counter. These results verify the feasibility of hydrodynamic analysis and provide an important basis for the optical measurement of high concentration aerosol particles.