Malicious attacks in the power system can eventually result in a large-scale cascade failure if not rectified in a timely manner. These attacks, which are traditionally classified into physical and cyber attacks, can be avoided by using the latest advanced detection mechanisms. However, a new threat called cyber-physical attacks jointly targets both the physical and cyber layers of the system to interfere with the operations of the power grid is more malicious than traditional attacks. In this paper, we propose a new cyber-physical attack strategy where the transmission line is first physically disconnected, the line-outage event is masked to mislead the control center into detecting this as an obvious line outage at a different position in the local area of the power system. Therefore, the topology information in the control center is interfered with as a result of our attack. We also propose a novel procedure for selecting vulnerable lines and analyze the observability of our proposed framework. Our proposed method can effectively and continuously deceive the control center into detecting fake line-outage positions, and thereby increase the chance of cascade failure because the attention is given to the fake outage. The simulation results validate the efficiency of our proposed attack strategy.