The exploration and improvement of excellent mid-infrared nonlinear optical (NLO) materials is still in great demand. The perovskite-type Sr2Nb2O7 is found to be a good predictor of NLO properties due to the similar band gap and NLO coefficients to KTiOPO4 (KTP). In this paper, we systematically investigated the electronic structures, linear and nonlinear properties of pure and V-doped Sr2Nb2O7 based on DFT. It is found that the V-doped Sr2Nb2O7 doubles the NLO coefficient and exhibits higher birefringence, which is moderate and sufficient for phase-matching. The results are helpful to the further development of the mid-infrared NLO crystals with perovskite structure.