With increase in use of technology along with new inventions, consumption of energy required is increased in exponential manner. In recent development of communication infrastructure in smart grids, it leads to new issues in physical power system related to cyber security. In traditional ways to handle cyber-attacks on power system, it generally involves separation of cyber domain and physical domain. Therefore, it is very important to have unification of cyber and physical power system. So to handle these issues, cyber physical power system (CPPS) is introduced. The CPPS mainly consists of core physical power system tightly integrated with cyber system. The purpose of CPPS is to monitor and control the smart grids efficiently and reliably. CPPS consists of various phases such as power transmission, power generation, power distribution, utilization of power, supervisory control and data acquisition system (SCADA), and utilization of power. These phases in smart grids are prone to cyber-attacks so it is important to summarize, analyze, and monitor cyber-attack methods on CPPS for the defense against different cyber-attacks. In this paper, we provide a comprehensive review of different kinds of cyber-attacks on physical power system phases. Also, paper analyzes various scenarios of cyber-attacks on systems and equipment such as SCADA system, smart meters, and communication system. Finally, according to several characteristics of cyber-attack methods, some preventions and detection methods are presented.