Abstract: According to the requirements of the American specification ASCE/SEI 7-22 for the fundamental period of structure, the fundamental period of boiler structural support steel was calculated by traditional approximate formula and structural analysis method based on STAAD.Pro software, and the fundamental periods of boiler structural support steel of different units were compared. Results show that, for the structural support steel of suspended boiler, the fundamental period calculated by the approximate formula method is shorter, and the fundamental period calculated by the STAAD.Pro software is longer than that obtained by the approximate formula. The fundamental period of boiler structural support steel is about 2 s for units with center support frame system, height of 70-100 m and capacity of 300-1 000 MW, which is similar to the calculation result of 1.4 times approximate formula. In the preliminary design stage, the 1.4 times approximate formula can be used to calculate the fundamental period for seismic design of large power plant boiler structural support steel. This method can not only ensure the safety and rationality of structural design, but also has good economic benefits.