This study develops numerical model of mega composite columns in fire and investigates the residual areas using 500℃ isotherm method and residual capacity of mega composite columns after 3 hours. In order to perform heat transfer analysis, thermal properties of steels and concrete were adopted from Eurocodes. In addition to, the temperature distributions of composite columns with respect to fire tests were compared with numerical analysis results. As a result, residual capacity of mega composite column with 1m width remained more than 45%. The residual capacity of mega composite column was only increased to 2.3∼2.6% with the use of additional rebars.