Abstract: A new framework of situation assessment oriented plan recognition (SAOPR) based on the closed loop of “Cognition, Prediction, Validation” is proposed for the application of situation assessment, and its implementing method has been researched too. In this paper firstly the workflow of the closed loop process is analyzed and the SAOPR framework is extracted. For to explain the describility and the calculability of the closed loop process, several concepts of situation elements are defined and the SAOPR architecture including the plan recognition algorithm is designed. Then the plan recognition knowledge model of SAOPR has been discussed. It is expectable for SAOPR to play a useful role in situation assessment system.