Abstract: For the output mode of speech synthesis which has been come true by using traditional D/A method, there is a lot of disadvantages, such as high discrete integrate resistance, nonlinear switching, high power dissipation. We propose a new method based on the theory of pulse width modulation (PWM), which convert directly the digital speech signal to the pulse width modulation wave and become analog speech signal by passing low-pass filter. Comparing with the traditional D/A method, the new method has the advantages of low power dissipation, high technique adaptability and high designing reliability. It has been applied in the chips of speech synthesis successfully.