Dynamic self-consistent field theory and Navier-Stokes equation are coupled to study hydrodynamic effects on the disorder-to-order transition of diblock copolymer melts. Simulations are performed for different values of the viscosity and the results are compared with those without the hydrodynamic effects. The lower the viscosity is, the faster the free energy density decays. Starting from uniformly mixed initial states, body-centered-cubic spheres, hexagonally packed cylinders, and lamellar structures are obtained in the presence of the hydrodynamic effects. On the contrary, the bicontinuous double gyroid structure cannot be obtained even with the hydrodynamic effects. The scattering intensities of the domain structures are calculated to confirm these properties of the ordering of the structures.