AbstractCold ions from the plasmasphere can reach the Earth's magnetopause through the plasma wind and plume, affecting the reconnection at the magnetopause, such as changing the reconnection rate and influencing the energy budget. Recent observations found that cold ions were substantially heated by magnetopause reconnection. Although a few mechanisms have been proposed to account for the cold ion acceleration at the magnetopause, the dominant mechanism remains unclear. In this paper, we perform 2.5‐dimensional fully kinetic simulations to study cold ion heating in asymmetric reconnection at Earth's magnetopause. We find that cold ions absorb about 10%–25% of the total released magnetic energy, which is predominantly converted into the thermal energy of cold ions. The proportion of the energy gained by cold ions increases with the increment of the initial density ratio of the cold ions to hot ions in the magnetosphere. Cold ions are primarily accelerated by the Hall electric field at the magnetospheric separatrix region, while the out‐of‐plane electric field does negative work. The increase in thermal energy of cold ions is mainly caused by stochastic heating, that is, the viscous heating associated with the non‐gyrotropic pressure tensor, , contributes the most. The work done by pressure is most significant around the magnetosheath separatrix region. These results can significantly deepen our understanding of the cold ion dynamics at Earth's magnetopause.