A study is conducted to improve the suction performance on suction devices which are used to remove polluted air generated by welding or machining process in a spacious working place of industries. The air suction duct which are using aircraft and industries require optimism shape and function by each usage. Air-curtain is applied around the suction inlet to blocking fresh air inflow from the downstream region. Two different type air-curtain devices, such as backward 180˚ and 135˚ are adopted. Suction region is investigated depending on the blowing mass flowrate to make air-curtain. Comparing the experimental results, the 135˚ backward air-curtain is superior to 180˚ backward type. When the injection and suction air velocity at 10 m/s , the suction area is improved to 38% compared to same condition of 180˚ backward case.