[Objective] Under the development background of high-proportion renewable energy integration driven by the "dual carbon" goals, the parallel operation of grid-forming energy storage converter (GFESC) has become the core solution for large-scale energy storage power stations. However, the inability to accurately allocate reactive power proportionally due to line impedance mismatch in parallel operation has emerged as a critical issue that urgently needs to be addressed. [Methods] The power transmission mechanism of the parallel converter system and the generation mechanism of reactive power allocation errors were first analyzed in depth through theoretical derivation. Based on this, an improved droop control strategy based on adaptive virtual impedance was proposed, aiming to dynamically compensate for the impact of line impedance mismatch on reactive power allocation. Finally, a parallel converter system model was built based on the Matlab/Simulink simulation platform, and the effectiveness of the proposed control strategy was verified through comparative experiments. [Results] The simulation results demonstrated that the proposed reactive power allocation strategy achieved high-precision proportional distribution under conditions where the actual line impedance was unknown and no inter-converter communication was required, while effectively reducing the output voltage deviation of the converters. After the introduction of virtual impedance, the strategy significantly mitigated the conflict between high-precision reactive power allocation and point of common coupling (PCC) voltage drop observed in conventional methods, enabling effective PCC voltage compensation to restore it to the rated operating level. Meanwhile, a double closed-loop control structure consisting of an outer voltage loop and an inner current loop is adopted to effectively maintain the stability of the system’s grid voltage and frequency. [Conclusion] The strategy achieves precise matching of equivalent impedance through adaptive virtual impedance, providing a highly reliable solution for the large-scale operation of GFESC.