Using a three-dimensional classical ensemble, we have investigated the internuclear distance (R) dependence of nonsequential double ionization (NSDI) of H2 molecules. In all alignments, as R increases, the double ionization (DI) rate first increases and then decreases, and it reaches its maxima when R is 4a.u.. The dependence of NSDI of H2 on R weakens as the angle between molecular axis and laser polarization(φ) increases. When φ is zero, the NSDI of H2 provides rich correlation patterns, which is strongly dependent on R. When φ is π/2, the correlation patterns are similar for different values of R and recollisions play a more important role in DI process. These results indicate that molecular structure has an important influence on NSDI of diatomic molecules.