Abstract: According to thin-wall component theory,equilibrium differential equations for C-and Z-purlins under wind-suction are derived,and finite element analysis is carried out.The result reveals that for Z-purlins,the twisting moment in the differential equation is very small,implying that the twisting deformation of Z-purlin under wind suction is very small,the thin-wall component theoretical results are in good agreement with those of the FEM analysis.The load-carrying capacity of Z purlin is greater than C-purlin of the same section size,and it is recommended that Z-purlins be used in precedence in practice