Considerable research has been conducted experimentally and numerically to investigate fire resistance of concrete-filled steel tubular columns exposed to uniform fire, whereas little research has been reported about fire resistance of concrete-filled square hollow section (SHS) columns subjected to 3-sided exposure. However, 3-sided fire condition may be very common in real structures because of layouts of walls. Knowledge of these columns is lacking and it may be unsafe to design the columns with current design provisions applicable for columns under 4-sided exposure. A sequentially coupled thermal-stress Finite Element (FE) model was developed and verified in this paper, and then it was utilized to analyze the differences of the same column under two different fire boundary conditions. The differences in thermal distribution, fire resistance and failure mode were compared and discussed. In addition, effects of geometric parameters on fire resistance were studied, including cross-sectional dimension and slenderness ratio. Finally, design recommendations were proposed to design concrete-filled SHS columns subjected to 3-sided exposure.