The material properties of aluminium alloys could be affected significantly as temperature rises. The present study aims to investigate the behaviour of aluminium alloy beams at elevated temperatures using finite element analyses. The newly developed numerical model was validated against a total of eight square hollow section beams subjected to three-point bending tests at elevated temperatures. The validated model was used to generate 120 numerical results in the parametric study. Three key parameters were considered, including cross-section slenderness ranging from 8 to 38, temperatures ranging from 24 °C to 600 °C and two aluminium alloys (6061-T6 and 6063-T5). Thus, a data pool containing a total of 128 experimental and numerical results was formed. The appropriateness of the design rules in the American Aluminium Design Manual, the Australian/New Zealand Standard, Eurocode 9 and the continuous strength method (CSM) for aluminium alloy beams at elevated temperature are assessed against the newly generated data pool. In comparison, the design strengths predicted by the four design methods are generally conservative, whereas the CSM approach is found to be the most accurate and consistent throughout the full temperature range. Additionally, reliability analysis has also been conducted to evaluate the reliability level of the aforementioned design methods for aluminium alloy beams at elevated temperatures.