Abstract: As the service life of the existing offshore oil platforms has been close to the end of their operational period, the dismantling, recycling and reusing of the marine platforms become a new technical challenge in the field of offshore engineering. Compared with the float-crane removal, the float-over dismantling has the advantages of no need of large lifting vessels and short cycle of operation so that it has been attached importance to and applied in the offshore platform dismantling projects. In this paper, the float-over dismantling process of the jacket platform on a catamaran is investigated. And based on this, the dismantling process is simulated and analyzed by establishing a dynamical model for the catamaran-topside system as well as by using multi-body dynamics software. The results show that the lifting arms show a good coordination during the dismantling process and have played a compensatory role to the motion of the topsides. Additionally, the results have also revealed the potential risk points in the dismantling operation process. Through the analysis of the float-over dismantling operation process, references can be provided for evaluating the performance of the dismantling operation and ensuring its safety.