Hardware-in-the-loop simulation (HILS) is an effective method to improve the accuracy of current large-scale power grid system simulating, and enhances reliability of the high voltage direct current/new energy device verification. First of all, on the basis of the basic architecture and its advantages of HILS for power systems, the technical characteristics and application of HILS in traditional power system are introduced, such as improving the accuracy of primary system modeling and reliability of secondary system controling. Then, the challenges of HILS application in the power system are analyzed and the key technologies for these problems solution are proposed, such as the flexible architecture technology for accessing multi-heterogeneous data models, the equivalent and the control system modeling of power system, and the universal interface technology for control object integration. Finally, from the perspectives of deep research on traditional technologies and new technologies development, the trend of hardware-in-the-loop simulation for power systems is discussed to provide valuable suggestions for development and validation of related platforms.