The materials and nanostructures derivated from graphdiyne have attracted much concern most recently.However the elongation effect from viewpoint of first-principle study for the polymerized graphdiyne building blocks is still exiguous,which would be great benefit to the understanding of structure-property relationship of the graphdiyne-based materials.This work presents first-principle simulations on the elongation effect of graphdiyne molecular chains with different lengths.The geometrical structures,relative stabilities and electron ic and nonlinear optical properties of the narrow chains obtained from graphdiyne are computed by using the Kohn-Sham self-consistent field molecular orbital method.