Abstract: Using the ultra-heavy-plate jet-impingement quenching test device and the multi-channel temperature recorder, 84 mm large section plates quenching temperature drop curve was experimentally investigated under the condition of jet velocities ranging from 3.39 to 26.8 m·s^-1, Reynolds number from 12808 to 117340 and jet densities ranging from 978.7 to 6751.5 L·(m²·min)^-1. Then, wall heat flux, heat transfer coefficient and boiling curve were calculated with inverse heat transfer modified method. The results indicate that both jet velocity and jet density influence the plate surface heat transfer mechanism and the distribution of the maximum heat flux. When jet velocity is low, a mixed heat transfer and "heat flux shoulder" phenomenon can be observed in wall parallel flow zone. With increased jet velocity, the film boiling heat transfer mechanism disappears and the maximum heat flux changes to the low-wall superheat position. These research results benefit the calculation of the temperature field and the control of structure property during ultra-heavy plate quenching.