Abstract: A new turbine film-cooling hole shape that is named the backward-expanding shoulder arm hole is designed. By using N₂ and CO₂ gas as the cooling gas, the film cooling perfor-mance with different density ratios of the backward-expanding shoulder arm hole, the circular hole and the shoulder arm hole is studied in the paper. The results show that, under the same conditions the film cooling efficiency of the backward-expanding shoulder arm hole is better than that of the circular hole and the shoulder arm hole, and the film cooling efficiency of the shoulder arm hole is slightly higher than that of the circular hole. The average film cooling efficiency decreases with the increase of the blowing ratio in the place where x/D < 15, and the average film cooling efficiency at Br=1.0 reaches maximum in the place where x/D > 15 when the density ratio is 1.0. The average film cooling efficiency increases first and then decreases with the increase of the blowing ratio, and the average film cooling efficiency is highest at Br=1.0 is maximum. The analysis indicates that as the outlet velocity is higher when the density is lower under the same blowing ratio, so that the cooling gas is more easily blown away from the cooling wall, the blow-ing ratio has effects on the film cooling efficiency of the backward-expanding shoulder arm hole.