Abstract: Two dose correction methods were compared for the under-response of EBT3 radiochromic films to the irradiation of mixed-LET carbon-ion beams. Carbon-ion beam of 260 MeV/u was used to obtain carbon-ion beams with multiple dose-averaged LETs by energy degraders. The films were irradiated by these carbon ion beams, and the optimal fitting formula was selected to fit the film dose response calibration curves. Relative Efficiency(RE) was used to quantify the under-response of EBT3 film with LET, and the doses of the films irradiated by mixed-LET carbon ions were corrected by the RE method. In addition, according to the relation between the fitting parameters of the dose response calibration curve and the dose proportions of different LETs, a new dose correction method was proposed and the doses of the films irradiated by mixed-LET irradiation were also corrected. Finally, the results of the two methods are compared, and it is shown that the dose deviation obtained by the fitting parameter method is less than 5%, which is better than the dose deviation obtained by the RE method less than 10%.