An apparatus and a method for loading a predetermined number of bits into a plurality of sub-channels are provided. The apparatus comprises a sort module, a calculation module, and a decision module. The sort module is configured to sort the sub-channels into a plurality of sorted sub-channels according to the quality value of each of the sub-channels. The calculation module is configured to calculate the difference value for each of the sorted sub-channels, except for the first sorted sub-channel, according to the corresponding quality value. The decision module is configured to decide a number of bits for each of the sorted sub-channels according to the difference values, wherein a summation of the numbers is equal to the predetermined number. The apparatus and the method are able to load bits efficiently according to the difference values.