Direct digital synthesis technology (DDS) is applied widely in synthesizing signal since it has characteristics such as high stability and wide frequency band. It is very important to calculate the phase control word when synthesizing dual signals with continuous tunable phase difference. Because there are shortcomings of large computation, low efficiency of phase setting, more storage space occupied or significant cumulative errors of phase setting when calculating phase control word with usual methods, three novel algorithms for calculating phase control word are developed in this paper. These new methods do not need large computation and more space and simultaneously they can decrease the error greatly, which play an important role in improving the phase setting speed and precision in dual signal generator.