Direct digital synthesis (DDS) is a digital synthesis technology that converts a series of digital signals to analog signals via digital to analog (D/A) converters. DDS function signal designing system consists of a phase accumulator, a waveform memory, a D/A converter and a low-pass filter. The design of phase accumulation and waveform memory is implemented by field-programmable gate array (FPGA), digital sequence is output, and the analog signals are generated via D /A converters and low-pass filtering. Using the oscilloscope to verify the waveform, the 5 KHz maximum waveform frequency of the single-chip circuit is enhanced to 20 KHz and the signal accuracy is improved. The scheme is verified by experiments and can be widely used in programmable systems.