Abstract: Dissipative particle dynamics(DPD) simulation method is applied to simulate the(microphase) separation behavior of two different four-arm star-diblock copolymers(A)_4(B)_4 and(AB)_4.(The p)hase diagrams are constructed according to the simulation results at different interaction parameters(between) A and B segments and the composition of the copolymers.It is shown that the phase diagrams(of m)ultiarm star-diblock copolymers are similar to those of the linear and cyclic diblock copolymers;i.e.,(the o)rdered three-dimensional mesoscopic structures,such as lamellae,perforated lamellae,bicontinuous(gyroid),hexagonal cylinders and body-centered-cubic spheres can be indentified in the parameter space. Some melted structures,such as micelle,liquid rod and random network phases have also been found in the phase diagrams,which can be regarded as transitional morphologies.Compared to(AB)_4,it is easier for(A)_4(B)_4 to begin phase-separating.One conclusion is that the molecular simulation on mesoscopic scale can be considered as an adjunct to relevant theory research.