In this paper, using all-speed preconditioned conjugate heat transfer numerical method and wind tunnel experiment, it is investigated the mechanism of the transient process that high speed hot airflow invades into gap-cavity sealing link structure. On the condition of porous material sealing in top gap of the linking structure, via the experimental method, it is found that there is existing increment-decrement-increment phenomenon of variation of temperature magnitude inside the cavity. Meanwhile this variation phenomenon could be reproduced by the all-speed preconditioned conjugate heat transfer numerical method and it is demonstrated that, the effectiveness of the numerical method established for this invading problem in this paper. Then by the numerical method, the more details with respect to the invasion process are shown to analyze the mechanism corresponding to this increment-decrement-increment phenomenon of variation of temperature magnitude. Finally, the symmetry and stability characteristics of the flow status with and without porous sealing are compared and the differences of the invasion process with and without sealing are further summarized. (C) 2015 Elsevier Ltd. All rights reserved.