Oxygen ions, O+, efficiently energized by weak fast shock in the mid-altitude cusp observed by Cluster on 7 November 2004 are investigated in this paper. An interplanetary fast shock hitting Earth magnetosphere was observed by Geotail at 1825 UT with a sharply increase in the solar wind dynamic pressure from 3nPa to 11nPa. There are significant fluctuations of solar wind dynamic pressure from 1930 UT to 2000 UT during this shock compressing Earth magnetosphere. During this pressure disturbance intervals Cluster 4 was located in the mid-altitude cusp, (0.43, -3.25, 3.07) RE_GSE. CODIF/Cluster 4 instrument detected O+ ions with tens keV energized by the weak fast shock with Mach number MA~1.2 in the perpendicular direction. Those energetic O+ ions have bunch or partial ring distributions in the mid-altitude cusp. Our observation results put forward confident evidences on the weak fast shock efficiently energizing heavy ions, especially, O+ ions in the cusp.