Abstract: Current design codes have not taken into account non-rigid effect of joints in determination of effective length of truss braces,but this effect cannot be neglected in some cases.Based on classic elastic stability theory of framework,the four-moment equation and the stability equations of member group considering joint rigidity are derived and extended to study trusses.Results show that the brace to chord stiffness ratio and the brace stiffness to joint rigidity ratio are two main factors influencing effective length of braces.Tables and simplified formulae computing effective length are proposed for practical design purpose.The significance of considering joint rigidity on effective length of compressive braces is demonstrated in an example of steel tube Warren truss with equal bay span.