The present invention provides a photoacoustic system and method for increasing light fluence. The photoacoustic system mainly comprises an ultrasonic device, an optical device, and a contact unit. The ultrasonic device emits an ultrasound toward a target tissue for generating a heat tunnel in the target tissue. The heat tunnel increases the light fluence in the target tissue, wherein the light intensity of the light emitted by the optical device is increased at a target point in the target tissue. |