In the analog modulation system,there are two kinds of frequency modulation method to sum up.The direct frequency modulation method can obtain large frequency offset,but frequency stability is low,temperature drift and time drift are relatively large;indirect frequency modulation method for frequency stability is high,but the circuit is very complex.Aiming at the lack of traditional analog frequency modulation method,theoretical derivation is made from the basic principle of signal frequency modulation,combinating the basic work principle of DDS technology to design,using FPGA to achieve the generated DDS FM signal.It focuses on the DDS modulation principle and circuit realization process.provides simulation and oscilloscope test chart FPGA designis.The whole hardware circuit unit is simple,the stability is good,the experimental results show that the design is effective.