An electronic device with a flash function and a driving method of a flash are provided. The electronic device includes a flash, an image sensor, and a processor. The flash has a red light source, a green light source, and a blue light source. The image sensor is configured to obtain a preview image of a current scene and outputting the raw data of the preview image. The processor obtains a red ratio value and a blue ratio value according to the current scene, and the processor determines the green brightness value, red brightness value and blue brightness value according to the red ratio value, the blue ratio value and an exposure sensitivity for obtaining the preview image. The processor drives the flash according to the calculated red brightness value, the calculated green brightness value, and the calculated blue brightness value.