In this paper, we discuss a modeling method and an altitude control system for a drone type UAV using the image information from the forward camera of the UAV. The model for the UAV dynamics is constructed based on the motion equation and the unknown velocity control logic which was made the internal organs in the drone system, and the parameters of the model are obtained by some experiments of the velocity constant control. The transfer function are expressed the 2 dimensional state space equation, and the optimal control method applied to the system include some limitation of the velocity control logic. This optimal control logic is realized as a PID control system. The P gain range of the PID controller is determined by the parameter of performance index of optimal control logic and the system keep optimal control feature in the range. By the experimental results, we confirmed that this system is stable and efficient.