Abstract: Distribution network security situation awareness is the key technology to comprehensively and dynamically analyze the security operation status and potential hidden dangers in the distribution network. For the rapidity and accuracy of security situational awareness in distribution networks, a novel method for security situational awareness in the distribution network was put forward based on synchronous phasor measurement units. Firstly, a hierarchical topology model of the distribution network was built to quickly capture system security situation elements under the premise of optimized synchronous phasor measurement units. Secondly, support vector data description algorithm with information entropy value was proposed to identify and understand the abnormal information in the security situation elements of distribution network. Thirdly, the long short term memory theory was used to predict the operation trend of the distribution network under normal and fault disturbance conditions, and then the zero-sequence voltage, voltage over-limit margin, branch overload severity and voltage phase change severity warning indicators were proposed to sense the real-time state and futuristic security risks. Finally, the validity of the proposed method was verified by typical IEEE33 and PG & E69 power distribution system. Simulation results show that the method improves the speed and accuracy of obtaining security situational elements of the distribution network, shortens the time for identifying abnormality of the security situational elements, and realizes the security situational awareness of each node in the distribution network.