The embodiment of the invention provides a method for processing an assignment message. The method comprises the following steps: receiving a Bitmap of an assignment message from a base station; determining bits corresponding to a removed MS in the Bitmap; and sequentially and inversely substituting the bits corresponding to the removed MS from the last bit of the Bitmap. The invention also provides with a terminal and a communication system. The invention adopts an inverse filling mode to reduce the number of moved bits so as to reduce the probability that the MS cannot receive the assignment message and the possibility of conflicts of different MS on the same resource and improve the spectral efficiency.