In order to accurately simulate the Doppler characteristics of high dynamic GNSS signals, a method for designing any-order DDS (direct digital synthesis) signal synthesizer was proposed. An any-order DDS synthesizer structure was designed; a formula for calculating the initial phase of every accumulator in DDS synthesizer was derived by using theoretical analysis; a technique to determine the DDS word length was developed. Finally, the simulation accuracy of the proposed method for the Doppler characteristics of GNSS signals was validated through simulations. In addition, since the proposed method for designing DDS synthesizer has no order limitation, it can be widely used in different types of signal simulators.