An architecture of direct digital frequency synthesizers (DDFS) has been studied in this paper. A new algorithm to reduce the size of ROM in the direct digital frequency synthesizer (DDFS) is proposed. The new ROM compression method can reduce the ROM size by using the two ROM and sine-phase difference method. To reduce the ROM size, we use the differential quantization technique with the sine-phasedifference. So the total size of the ROM in the proposed DDFS is significantly reduced compared to the original ROM. The ROM compression ratio of 68% is achieved by this method. Also, the power consumption is affected mostly by this ROM reduction.