The measurements based on flow characteristics have been playing more and more important roles in the analysis of Network Behavior. As a main method of flow recognition, the timeout strategies have a very important impact on the correctness and performance of flow measurement. This paper firstly discusses the state-of-art of flow timeout strategies, and points out where they are applicable and their shortcomings. To deal with the short flows that take a large part of the total flows in the networks, the paper presentes a Dynamical Timeout Strategy (DToS) based on the analysis of flows’ length distribution and flows’ rate metrics in detail. This method could improve the performances of network measurement and the efficiency of the resource usage in measurement systems by using different timeout strategies dealing with flows that have different rate features based on analyzing the usage of target network. It could also apperceive network abnormal behavior efficiently, and trigger emergent methods to ensure the safety of measurement system. After that the feasibility and robustness of this method are analyzed. At last, some experiments are employed to show the rationality of DToS strategy. The fitness area of strategy is also anatomized in the paper.