Radar technology first appeared in 1842, proposed by the Austrian physicist Doppler. Over time, radar has had different applications in many fields. Among them, the use and advanced degree of radar in the military field is the highest. It was used to detect enemies to attack or defense. In recent decades, a more advanced phased array radar can replace the traditional radar in the military. In this report, it is focused on the principle and function of phase array radar and the applications and development of it are also discussed. Research on current phased array radar will help to develop higher performance and lower power consumption radar in the future. Combining the advantages and disadvantages of phased array radar helps to have a clearer view on the future direction of radar research.