A molecular dynamics simulation of 4, 4'-dichlorobiphenyl sulfone was carried out in order to study the phase transition from a normal to incommensurate modulated phase observed experimentally. Agreements of simulated and experimental diffraction patterns and lattice constants indicates that the simulation is able to well reproduce the normal-incommensurate phase transition. The incommensurate modulation is found to originate from large-scale fluctuations in the displacements of the molecules.