Abstract: To investigate the influence of two parameters of cable pretension and diameter，on the seismic behavior of a steel mega frame and cable-braced structure and obtain appropriate values of these two parameters，the Pushover analyses were made for typical steel mega frame and cable-braced structures with different pretensions and diameters of cables． It was examined the effects of different cable pretension and diameter on the failure modes，initial lateral stiffnesses，ultimate loads，top displacements and the base shears at performance points，and maximum inner-story drift angles of the structure，it could be found that the cable pretensions only have a limited impact on the maximum inner-story drift angle，and their influences on other comprehensive performance of the structure could be ignored， and the cable diameter had a small impact on the failure mode when its increment did not exceed 100%，but the cable diameter change had significant effect on the other comprehensive properties．