Abstract: The present invention relates to a direct digital frequency synthesizer using a variable sine wave-weighted digital to analog converter with improved size and efficiency and a synthesizing method thereof. The direct digital frequency synthesizer and the synthesizing method thereof are capable of simplifying a configuration for matching output data of a phase accumulator to sine wave amplitude without increase in complexity of a DAC by applying a nonlinear DAC for directly generating a current corresponding to base points with sine weights and a variable sine wave-weighted DAC for generating fine currents to be combined with variable weights based on the base points. Accordingly, it is possible to provide a high quality output, reduce a size and power consumption, and increase a speed.