Aimed at the limitations of total fluctuating wind-induced response with combination of background and resonant components using Square Root of the Sum of Squares (SRSS) method, the theoretical combination formulas of fluctuating wind-induced responses and ESWLs are derived based on structural dynamics and random vibration theory. Meanwhile, the refined analysis method is firstly presented by four components formula to compensate the coupling component between background and resonant modes. The proposed procedure avoids the integration process of calculating elastic restoring force and completely considers the modal coupling effects, which can be used to calculate the ESWL for any complex structures. Taking the steel grid roof structure of a large museum as an example, the new method was used to calculate its wind-induced response. Compared with results of complete quadratic combination (CQC), the effectiveness and accuracy of the present approach has been revealed.