Curve 1 achieves very excellent small-flow stability. At design point Q=10m3·h-1 and rotating speed n=8500r·min-1, efficiency η1=34.6%, head H1=420m, and the head coefficient 1 φ =0.542. But curves 2 and 3 don′t achieve small-flow stability. When Q=10m3·h-1, H2=415 and H3=406m, and η2=30.5% and η3=26%, φ 2=0.534 and φ 3=0.523. In addition, due to severe fluctuation in the small capacity region, the head and