A quadrocopter is a multicopter that is lifted and propelled by four rotors. Nowadays the development of autonomous quadrocopters has been in the focus of researchers. This thesis examines a quadrocopter's navigation system in a simulated environment. This navigation system is able to navigate through an unknown 3 Dimensional terrain until it reaches its final destination. The most important factor during the helicopter's flight, is its ability to avoid obstacles in its path and to avoid collisions. The thesis explains certain unique situations (navigation in a dead-end region, avoiding moving objects, moving between object through narrow spaces) and contains suggestions and solutions to these problems. Afterwards the thesis deal with ultrasonic sensors' simulation and examine the helicopter's path with changing of the sensors' parameters. The thesis discusses the rotate of the quadrocopter around its vertical axis. Finally the thesis demonstarte the helicopter's flight path through a varying obstacle course and mentions other development and modification options.