In this article the authors propose a trajectory control algorithm for an unmanned aerial vehicle (UAV), which is lifted and propelled by four rotors. The first step in designing of the above mentioned trajectory controller was development of a quadrocopter flight dynamic (math) model and its further linearization. The math model was based on Newton and Euler equation of motion. The next step was designing of a quadrocopter attitude control on the grounds of a linearized dynamic model and angular PD regulator. Then the authors were able to elaborate a trajectory control algorithm by using PD regulator for a trajectory error minimization. Finally, in order to verify the control algorithm the authors built a control system model in Matlab, designed a dynamic model in Universal Mechanism for flight simulation and conducted several experiments. The key idea of the developed trajectory control algorithm is that the control inputs are forces and momentums applied to a quadrocopter, as dynamics of the motor and propeller pairs are essentially faster compared to the rigid body dynamics. One of the major objectives in the attitude control design was to avoid the angels' subtractions in order to prevent singularities. For this reason the authors used rotation matrix error and PD regulator instead of Linear Quadratic Regulator. A set of experiments in the Universal Mechanism and Matlab proved the efficiency of the developed trajectory control algorithm. The paper also presents the modeling details and experiment results.