In order to reveal more information and understanding on behavior and failure mechanisms of high strength steel Q690 endplate connection after fire, a fullscale experimental study has been carried out after cooling down from fire temperature 550°C. Further, their behavior was compared with the provisions of Eurocode 3 and the test results obtained from the experimental study on the high strength steel endplate connections without fire exposure. The research shows that the failure mode of high strength steel Q690 endplate connection after fire is bolt failure with yielding of the flange, and their rotation capacity is sufficient. What is more, using accurate postfire mechanical properties, the component method which Eurocode 3 proposed based on connections made of mild steels can be used to calculate the plastic resistance and to predict the failure mode of high strength steel endplate connections after fire, but it is not suit to predict their stiffness. Furthermore, they can regain more than 90% of its original load bearing capacity after cooling down from fire temperature 550 °C. Moreover, a series of formulations are presented for judging the failure mode of high strength steel endplate connections post fire.