In order to reveal the bearing mechanism of doubling plate- reinforced square tubular joints under axial compression,monotonic loading tests of the joints were carried out,and the failure modes as well as the load-deformation curves of the specimens were analyzed.Then,a finite element model of the joints was constructed,and the corresponding model parameters were analyzed,through which the reinforcement mechanism of doubling plate for joints was revealed.Moreover,the formulas of bearing capacity of doubling plate- reinforced joints were deduced based on the yield line method,and some design proposals were suggested for the doubling plate reinforce-ment.The results show that (1) the compression capacity of the joint significantly improves with the thickness of the doubling plate but changes a little with the plate width and length; (2) the reinforcement ratio of doubling plate increases with the decrease in brace- chord width ratio β; (3) the doubling plate improves the compression capacity by yielding together with the chord flange; (4) when β≥0.8 or when the plate thickness exceeds a certain range,the yield of doubling plate may be incomplete due to the buckling of chord web; and (5) the deduced design formulas accord well with the results of experiments and parameter analyses.