With I2C bus structure, PCF8591 Digitaltoanalog converters controlled by STC15F2K60S2 single chip microcomputer, generating sine wave, square wave and triangular wave. Through switch K1, it could change waveform. It could also increase and decrease of the frequency with switch K2 and K3. Finally, it outputs 5 V adjustable frequency, and the frequencies and names could reveal on liquid crystal display in different waveforms. And, by using software of Proteus to simulate waveform generator, it find that actual production circuit are basically identical. This kind of waveform generator is easy to handle, which operation is stable and reliable and its output waveform can meet the requirements of teaching and the electronic measurement.