Using the semiclassical rescattering model, we have studied the effect of molecular internuclear distance on non-sequential double ionization. In the process of our analysis, the non-sequential double ionization rate, two-electron ionization energy, two-electron momentum correlation and the combined potential of Coulomb field and laser field are calculated with the molecular internuclear distance changing. The results show that non-sequential double ionization rate and the double ionization events with the sum of the two electron momentums equal to zero increase with the molecular internuclear distance increasing when the molecular internuclear distance is within 1.0—6.0 a.u. When the molecular internuclear distance continues to increase (greater than 6.0 a.u.), non-sequential double ionization rate and the double ionization events with sum of two electron momentums equal to zero decrease.