To implement the objective of smart grids， it is essential to introduce the state of the art computing， communication and sensing technologies， and seamlessly integrate them with the power system. The cyber physical system（CPS） is an emerging but highly important research area concerning the deep integration of physical and information systems. In this work， based on the concept of the CPS and taking into account the characteristics of power systems， the cyber physical power system（CPPS） is proposed. The concept， main functionalities and technical characteristics of the CPS are first introduced. The architecture and major components of the CPPS are then illustrated. Next， some important techniques for developing the CPPS are clarified. Finally， several important research problems associated with the CPPS， including the theoretical foundation， system modelling， simulation algorithms， security assessment， reliability assessment， system design and planning as well as system operation， and the standardization of CPPS， are presented.