Abstract: A camera system with function of automatically coordinating flash intensity includes a lens, an image sensor, a focus system, a focus sensor and a control unit. The lens is capable of controlling light amount that entrance into camera. The focusing system is capable of driving the lens to focus thereby forming a clear image on the image sensor. The focus sensor is capable of sensing first step information of the focusing system during the focusing process, and sending the information to a control unit. The control unit is capable of transforming the result of the focusing system to a distance that the object apart from the camera, and configures out the guide number with the aperture number thereby calculating the flash intensity. The present camera systems without neither a professional measurement tool nor an additional pre-flash may measure the distance that the objects apart from the camera, and low down the cost and power consumption.