The construction of underground cavern groups of pumped storage power plants is facing the difficulty of effective ventilation, and the wind-dust migration in the caverns shows no significant characteristics. In view of this, a gas-solid two-phase flow discrete phase model is adopted for the numerical experimental research of long and straight tunnels with different slopes in underground cavern groups, which focuses on revealing the migration rule of wind-dust and the distribution characteristics of small-size settling dust in typical tunnels under different construction conditions. The results show that the dust mass concentration in different areas decreases with the increase of the fan wind speed, and then starts to increase when the wind speed researches 21 m/s; whereas the dust mass concentration in the area near the tunnel face increases with the increase of the air supply distance, however when the air supply distance is greater than 25 m, the fan wind speed can no longer meet the ventilation requirements of the tunnel. The dust mass concentration in the area near the tunnel face increases significantly with the increase of the tunnel slope, which leads to an obvious dust blank zone near the wind duct. The distribution characteristics of small-size settling dust are determined by the wind duct position, and the most settling dust particles are located between the duct outlet and the tunnel face. The particle sizes are widely distributed in this area with a normal distribution law, and the particles decrease sharply at the right rear of the duct outlet, but gradually along the direction of the tunnel outlet, so does the average particle size. The average size of the dust particles flowing out of the tunnel is relatively small. This study can provide some reference for the overall construction design of underground cavern groups of pumped storage power plants.