Abstract: For the purpose of investigating the influence of high-pressure grinding rolls (HPGR) ul⁃ tra-fine crushing technology on the grindability of Heishangou iron ore from Shaanxi，tests including open-circuit HPGR crushing，closed-circuit HPGR crushing，and pre-concentration tailings discarding were carried out by using the fine crushed product（16~0 mm）from the beneficiation plant. Open circuit roller pressing tests showed that increasing the roll surface pressure could improve the fines yield，while the roll speed had little effect on the product particle size. Under closed circuit conditions with a roll sur⁃ face pressure of 9 MPa and a screen aperture of 3.0 mm，the circulating load was 61.50%，the throughput was 32.3 t/h，the unit energy consumption was 2.04 kW·h/t，and the -0.075 mm content in the undersize product reached 28.86%，indicating good ultra fine crushing performance. In the pre-concentration tests， dry magnetic separation of the oversize product could discard tailings with a yield of 17.45% and a magnet⁃ ic iron grade of 0.92%，while the magnetic iron recovery of the concentrate was 99.36%; wet magnetic sep⁃ aration of the undersize product could discard tailings with a yield of 38.49% and a magnetic iron grade of 0.45%，with a magnetic iron recovery of 99.23% for the concentrate，and the feed iron grade increased by 12.28 percentage points. Relative grindability tests showed that the wet magnetic separation concentrate from the HPGR undersize was easier to grind than the run-of-mine ore; when both were ground to 60% passing 0.075 mm，the relative grindability coefficient was 1.08. The HPGR-pre-concentration process can significantly improve ore grindability and achieve effective tailings discarding，thus it can serve as a basis for energy saving，consumption reduction，quality improvement and efficiency enhancement in the beneficiation plant of Heishangou Iron Mine.

Key words: HPGR, iron ore, relative grindability