The invention discloses a frame bias-allocating method of CDMA mode communication system in mobile communication field, for cluster calling, firstly inquiring about a database stored with frame bias use situations, selecting an unallocated frame bias from the retained frame biases: if there is no unallocated frame bias, select a lowest-load frame bias and if all the retained frame biases have the same load, arbitrarily select a frame bias for allocating; for private calling, according to time delay and SDE frame bias, determining several frame biases of channel units, selecting an idlest frame bias for allocating and modifying the use information of this frame bias in the above database. It can avoid the reduction of processing ability of a chip caused by centralized allocation of frame biases and that of the system capacity, effectively enhancing the processing ability of the chip and channel plate and increasing the system capacity.