Abstract　 　　  

   In this talk, we discuss the dynamical fate of planetary systems due to environmental and internal factors, respectively. Firstly, we carry out N –body simulations to examine the effects of dynamical interactions on planetary systems in young open star clusters. We explore how the planetary populations in these star clusters evolve, and how this evolution depends on the initial amount of substructure, the virial ratio, the cluster mass and density, and the initial semi-major axis of the planetary systems. These results help us to obtain a better understanding of why the observed number of exoplanets in star clusters is relatively low, and allows us to make predictions about the free-floating planet population over time in different types of star clusters and in the Galactic field. Secondly, we focus on the internal dynamical evolution of planetary systems in depleting gas disk. We consider the possibility that a major fraction of the original asteroids population may be cleared out by Jupiter’s secular resonance as it swept through the main asteroid belt during the depletion of the solar nebula, providing a natural explanation for both of the observed low surface density and size distribution of asteroids in the main belt without the need to invoke some special planetesimal formation mechanisms. We further investigate how secular perturbations by the gas giant can induce the formation of gaps in circumstellar debris disks, and providing possible explanation for the eccentric architecture in some hierarchical system.