Abstract: The responses (e.g. bearing initial displacement) and dynamic characteristics (e.g. modal frequency) of long irregular base-isolated structures (BIS) vary with environmental temperature variation. Based on monitoring data including the temperature of isolation layers, horizontal displacement of isolation bearings and acceleration response data of the superstructure of a long irregular BIS, the rule of horizontal displacement of isolation bearing and dynamic characteristics affected by environmental temperature variation are investigated.The mechanism of environmental temperature's effects on the horizontal displacement of isolation bearing and dynamic characteristics of BIS is analyzed theoretically. The dependency between the horizontal displacement of isolation bearing and environmental temperature is studied. Meanwhile, combining the conclusion of the dependency experiments of isolation bearing with temperature variation, the results of the dependency analysis of environmental temperature's effects on the dynamic characteristics of BIS are validated. The results show that the environmental temperature and the horizontal displacement of isolation bearing showed relatively strong dependency. The conclusion of dependency analysis using monitoring data is consistent with the dependency experiments of isolation bearings. Finally, the dependency models of the horizontal displacement of isolation bearings and modal frequency with environmental temperature variation and the curves of influence coefficients of environmental temperature affected on modal frequency are proposed. The basis of assessing the performance of BIS reasonably and accurately is laid.