Abstract: The construction of the new power system with renewable energy sources as the main power sources is a key technical route to realize the strategic goal of carbon emission peak and carbon neutrality. In the context of the development of the new power system, with the integration of high proportion of renewable energy sources, the evolution of transmission and distribution forms of the power system leads to highly power-electricized system. The very different operation characteristics and fault features lead to serious challenges in the traditional fault analysis method and the principle action performance of relay protection with the synchronous generator source as the fundamental and the linear superposition principle as the theoretical basis. This paper systematically describes the key problems faced by the traditional fault analysis and relay protection in the typical scenarios of the new power system, and then elaborates the solution ideas from the perspective of the fault characteristic and law cognition of the new power system, the adaptation boundary and performance enhancement technology of the traditional protection, the new principle of relay protection independent of source characteristics, and the control and protection coordination for actively supporting protection demands of power electronic equipment.