Direct digital frequency synthesis (DDS) technology is a new type of frequency synthesis technology. It has a higher frequency precision, which can not only achieve frequency switching quickly but also ensure the continuity of the phase when the frequency is changing. However, the output waveform and frequency range of special DDS chips are usually fixed. We extend the structure of DDS circuits by adding some modules such as data distributor, ROM for storing different waveform data, and peripheral control circuit module based on the research on special DDS chip circuits. Thus variablefrequency multimode signals are generated. The whole variablefrequency signal system is integrated on the large scale programmable FPGA chip to achieve waveform programming and frequency programming. Meanwhile, it can not only realize waveform selection such as sine wave, triangular wave, sawtooth wave, square wave, etc., but also change the frequency of each waveform. The system integrates many modules such as the PLL frequency multiplier, frequency divider, data selector, data distributor, frequency word input module, DDS signal generator, and key module on the programmable FPGA chip, which greatly improves the integration and reliability of multimode variablefrequency signal circuits. Due to the programmability of the FPGA, the system parameters can be adjusted through field programming, which increases the flexibility of circuit adaptation.