Unmanned aerial vehicles (UAV) are currently being applied in many fields today, from military to civil. Mastering the technology of manufacturing and controlling UAVs is currently an important task for each country. In controlling a UAV, keeping it at a stable altitude is challenging due to nonlinearity and fluctuations in environmental factors. With simplicity but effectiveness in design, the PID controller chosen for research in the article aims to respond quickly and accurately to changes in altitude, helping the UAV achieve and maintain the desired altitude. The effectiveness of this method has been verified through simulation and practical tests with a self-made and assembled the UAV prototype. The results show that the PID controller can ensure stability and high accuracy in maintaining the altitude of the UAV. The experimental results have demonstrated the feasibility and effectiveness of the PID controller in these real conditions.