In this paper, we present a mesoscale simulation method for heavy petroleum combing structural unit (SU) and dissipative particle dynamics (DPD). We proposed 16 basic SUs, which represent the basic structural fragments for heavy petroleum molecules. The SUs were then used as beads in DPD simulation. The process for bead partition and DPD parameter calculation were described. The presented method links the molecular compositional modeling with mesoscale modeling via a chemical-defined mapping process. The equilibrium state of aromatic hydrocarbons with different ring numbers was simulated by the SU-DPD method, proving that the self-assembly behavior of polycyclic aromatic hydrocarbon systems can be properly revealed. On this basis, we built the SU-DPD model for heavy petroleum in terms of averaged four-components molecules. Various heavy petroleum systems were simulated at a coarse-grained level, including pure asphaltene system, asphaltene-toluene system, heavy petroleum system, and heavy petroleum-water system. The simulation results were consistent with the Yen-Mullins model and experimental results.