For the purpose of knowing the motion law of sand erosion and improving the efficiency of cyclone separation sand sampler, the finite element model of cyclone separation sand sampler is built by using the software of Fluent. There is a two-phase movement inside the cyclone separation sand sampler, including air and soil particles. The cyclone separation sand sampler mainly separates the soil particles from the air. Since the concentration of the soil particles is not too high, its movement inside the sand sampler depends largely on the gas phase (air) movement, and a majority of the particles flow with the air. Due to the above-mentioned reasons, it is necessary to make further analysis on the air flow inside the cyclone separation sand sampler. Boundary conditions are of great importance to the simulation of the gas flow inside the cyclone separation sand sampler, and the gas phase has been simplified: the gas in the sand sampler is air, with a density of 1.225 kg/m3 and a viscosity of 18.1×10-6; it is treated as incompressible gas, and its flow is treated as in steady state; the exit is set for free outflow; the wall surface is set as no skidding and no moving surface; the 2 surfaces overlapped by the ascension pipe and the barrel of the sand sampler are set respectively as Interface for data exchange; the upper part of the sand sampler and the sandbox are sealed well, without gas flowing out; the straight pipe connecting the cone-shaped part and the sandbox is 10 mm long; the hydraulic diameter is 0.015 mm, the Reynolds number is 1.02×104 and the turbulent intensity is 5.1%. Based on the RNG k-ε model and the Reynolds stress model, numerical analysis is carried out for the cyclone separation sand sampler. Besides, some wind tunnel tests are made for 3 cyclone separation sand samplers with different structure parameters. The internal motion law of the gas phase is found through the finite element analysis; current field intensity near the gas exit tube of the sand sampler is stronger and the "shunting flow" exist inside. At the same time, by the numerical simulation of 3 cyclone separation sand samplers with different structure parameters, the results show that the sand sampler with cylinder diameter of 50 mm, and cone height of 125 mm has the smaller turbulent kinetic energy 0.99 m2/s2 and the maximum upward axial velocity 1.48 m/s in sandbox bottom. In addition, the wind tunnel test is done with 3 different structural parameters of the cyclone separation sand sampler, and the experimental results show the turbulent kinetic energy of sandbox bottom which has certain impact on the trapping efficiency is changed with cylinder diameter and cone segment height. Compared to cylinder diameter, cone segment height has greater influence on the efficiency of the cyclone separation sand sampler. The cyclone separation sand sampler has better separation performance and higher trapping efficiency when the turbulent kinetic energy and the upward axial velocity of sandbox bottom are lesser. Through numerical simulation and wind tunnel test, the objective function is determined by the turbulent kinetic energy and the upwards axial velocity of the bottom of sandbox. The length of the straight tube of sandbox is optimally designed through the objective function. The efficiency of cyclone separation sand sampler can be improved while the straight pipe of sandbox is 16 mm. The results can provide the basis for further enhancing the performance of cyclone separation sand sampler.