When a short-circuit fault occurs on the collection line through which renewable energy is transmitted via a modular multilevel converter-based high-voltage direct current (MMC-HVDC) stations, the short-circuit currents supplied by power electronic converters on both ends of the line are mutually coupled. This coupling leads to random variations in fault characteristics, making accurate calculation difficult and complicating protection setting and coordination. Consequently, new methods for short-circuit current analysis and calculation are urgently needed. Existing short-circuit current calculation methods do not adequately account for the coupling effects between renewable energy sources and MMC-HVDC converters, and thus cannot ensure sufficient accuracy during transient states. To address these limitations, this paper proposes a novel analytical approach that adopts a linear partitioning concept to decouple the interaction between renewable energy sources and the MMC-HVDC station. A mathematical method based on sequence admittance substitution is proposed to indirectly obtain an analytical expression for the fault point voltage. The MMC-HVDC side fault current is then derived through current-voltage mapping relationships. A test system in which a renewable energy collection system is connected to an MMC-HVDC station is established on a hardware-in-the-loop experimental platform. By comparing the calculation errors of the proposed method with those of conventional methods under various fault scenarios, the results demonstrate that the proposed method maintains calculation errors below 5%, thereby verifying its effectiveness.