The invention provides a digital modulation method and a digital modulation device, so as to carry out digital modulation on the to-be-inputted original data set of a cascaded filter bank including an up sampling module, realize compression on the data number in the original data set and improve the spectrum performance and the bit error rate performance of the system. The method comprises steps: the number of to-be-compressed data in the original data set is determined; the data in the original data set are divided into a first data group and a second data group, wherein the sum of the number of data symbols included in the first data group and the number of data symbols included in the second data group is equal to the difference between the number of data symbols obtained when the data in the original data set is divided according to a first digital modulation order and the number of to-be-compressed data in the original data set; and the first digital modulation is adopted to modulate the data symbols in the first data group to obtain a first modulation data group, and second digital modulation is adopted to modulate the data symbols in the second data group to obtain a second modulation data group.