Abstract: This paper summarizes the challenges to the simulation of the new power system, brought about by the characteristics of high penetration of new energy generation and high penetration of power electronic equipment, and proposes the design concepts for the power system simulation software development, i.e., the six aspects of the complete models, accurate modeling, efficient computation, comprehensive scenarios, open interface, and flexible services. Then, based on the awareness that simulation is just an approach rather than the purpose for understanding and reforming the new power system, and that the simulation should adapt to the digital transformation needs of power enterprises in the background of the new power system, it is pointed out that the function orientation of China’s independent power system simulation software should be transitioned from simple simulation tool to power system simulation software development platform and operation environment, and a development path is proposed that helps users automate their business procedures, facilitate their platform use and ecologize the application development. Finally, the guiding roles of the above design concepts and development path are illustrated by the introduction of the developed simulation software development platform and operating environment for the new power system, i.e., CloudPSS.