Control of type-I ELMy H-mode by pellet injection is numerically investigated for KSTAR and ITER. Inverse proportionality of pellet-induced edge localized mode (ELM) energy loss to pellet injection frequency is found to be similar with spontaneous ELMs in KSTAR. Pellet injection frequency is proposed to be a key parameter to control the ELM frequency and resultantly the ELM energy loss. Extending KSTAR modelling, a pellet-induced density perturbation model is applied to the ELMy H-mode discharge of ITER so that the control of type-I ELMy H-mode by pellet injection is demonstrated to check the availability of pellet ELM pacing for mitigating ELM peaks in ITER. The simulation predicts that 25 MJ of energy loss could be released by type-I ELM in ITER which exceeds the material limit of plasma-facing components (PFCs). However, the ELM pacing simulation indicates that pellet injection from high-field side and low-field side in ITER can significantly mitigate the ELM energy loss by up to a factor of 7.35 at 20 Hz of pellet injection. The performance of pellet pacing is expected to be effective but still might be insufficient to satisfy engineering restrictions of PFCs. Further improvements of mitigation performance will be required to achieve fully controlled ELMy H-mode plasmas in ITER.