The invention discloses an online marking method for a three-dimensional model component. The method includes the following steps that preprocessing is conducted, and features and over-segmentation pieces of triangular patches are obtained; initial marking is conducted, a segmentation model is initialized, seed area marking is conducted on an initial three-dimensional model which is input by a user, a seed marking set is obtained, online learning is conducted on the seed marking set, and the partition model is learned; online marking is conducted, the segmentation model is used for conducting segmentation marking on an input three-dimensional model of the same type, a middle marking result is obtained, whether the result is approved or not is judged by the user, if yes, the process is over, and the middle marking result is a final marking result, and if not, the user conducts area correction on the middle marking result, the seed marking set is obtained, online learning is conducted on the seed marking set, the segmentation model is updated, the updated segmentation model is used for conducting segmentation marking on the three-dimensional model, the middle marking result is obtained, continuous iteration is conducted until the middle marking result is approved by the user, and the final three-dimensional model marking result is obtained.