Abstract: It has become a typical scenario in the power system that the renewable energy power is connected to the AC system through the flexible DC transmission line. Taking the positive sequence voltage-polarized phase-comparison distance protection of the AC line connected to the receiving end of the modular multilevel converter-high voltage direct current (MMC-HVDC) as the object, while considering the control strategy of the MMC-HVDC, this paper analyzes the performance of the distance protection when the short-circuit fault occurs on the AC system. The distance protection may refuse to operate when the internal fault occurs and mis-operate when the external fault occurs. In order to explore the mechanism of the incorrect operation, the influence of parameter changes for operation of distance protection is analyzed on the voltage plane, the inherent constraints of power angle and short-circuit capacity for distance protection are revealed, and the power angle boundary for correct operation of distance protection is deduced. By equating the MMC-HVDC system reasonably, the control strategies of the inverter increase the equivalent power angle of the system when the internal short-circuit fault occurs on the AC line. The performance of distance protection is on the boundary, which means there is a risk of non-operation/mis-operation. A typical scenario simulation model of a new power system is established by RTDS, the equivalent power angle characteristics of the system for the AC line fault are analyzed, and the incorrect operation of distance protection is verified. The fault of the AC line at the receiving end are analyzed, and the incorrect operation characteristics of the distance protection are verified.