In order to investigate the spatial distribution difference of the reliability about steel truss structure of 623Journal of Vibration， Measurement ＆ Diagnosis Vol. 44 terminal building under dynamic actions， the calculation equation of structural failure probability with approxi? mate extreme-value（ ΔPi） as characteristic variables are derived based on the extreme-value（ P） at the principle of equivalent extreme-value. Combined with the optimization case of steel grid structure in an airport， the struc? tural reliability laws of steel roof under different effective peak acceleration （EPA） are analyzed by numerical simulation， and the superiority of the improved equivalent extreme-value method in predicting structural failure is summarized . The results show that the upper and lower bound curves of structural failure probability obtained by the improved equivalent extreme-value method can accurately represent the variation trend of "three stages" of structural failure under different EPA， and the calculation threshold converges with the increase of EPA and ap? proaches zero when EPA is greater than 0.22 g. When the optimization indexes of structural design satisfy the re? quirements of the code， the cantilever structure arrangement at the end of the corridor makes its dynamic reliabil? ity significantly weaker than that of the surrounding structures， which indicates that the improved equivalent extreme-value method can not only effectively predict the structural reliability trend， but also has higher predic? tion accuracy. In addition， the failure probability of support nodes in the corridor structure section is close to the overall failure probability， and the error is less than 4% when EPA is less than 0.295 g. Therefore， the overall reliability of the structure can be monitored by only supervising special nodes.