Abstract: This paper discusses the finite-volume effect in calculating hadron form factors using lattice QCD framework. Taking Pion as the example, we introduce the method of extracting hadron form factors from three-point correlation functions computed in lattice QCD, but only at separated points in the momentum space because of the finite-volume effect. This paper gives one interpolation algorithm which respects rotation symmetry and also provides a sketch of another interpolation method which applies the continuous Fourier transform, both methods continuously giving form factor results on the momentum space based on the discrete values. These algorithms are examined under numerical models and realistic lattice systems. The results given by the interpolation are independent of specific systems and can be easily generalized to a variety of lattice systems. Our conclusion also provides valuable information which could help determining the proper size of lattice systems.