In the present study, various groove casing treatments were evaluated under a high-speed subsonic axial flow compressor using experimental and numerical simulation methods. The aim of this study was to explore the effect of inclination of grooves on compressor stability and performance. The potential flow mechanisms were also evaluated. Three different inclination grooves were designed in this study: grooves with no inclination, grooves with 30 degrees upstream inclination and grooves with 30 degrees downstream inclination. Similar effect of the grooves on the compressor stability and efficiency was observed under experimental and numerical analyses. The grooves with no inclination, 30 degrees upstream inclination and 30 degrees downstream inclination enhanced stall margin by 6.08%, 8.74% and 3.03%, respectively. The peak efficiency losses of the three types of grooves were 1.62%, 0.94% and 2.33%, respectively. Tip flow field analyses demonstrated that the radial transport effect caused by grooves effectively reduced tip loads and alleviated tip blockage. This explains why the grooves enhanced the compressor stability. The radial transport effect was enhanced, and a larger stall margin improvement was obtained when grooves inclined upstream were applied. The tip flow loss was the dominant loss observed after grooves were applied on the compressor. The grooves with upstream inclination markedly reduced the tip flow loss, indicating that they exhibited the lowest effect on reducing compressor efficiency compared with the other types of grooves.