Abstract: With the advancement of DC transmission, both LCC-HVDC and VSC-HVDC systems will inevitably integrate into the same regional grid. This integration has led to the formation of hybrid multi-infeed DC transmission systems in some areas of China. The layered access method for LCC at the receiving end can enhance the voltage support capability of these hybrid systems. However, in UHVDC transmission projects employing hierarchical connection modes at the receiving end, a commutation failure in the valve group of one layer may induce a commutation failure in the valve group of a non-faulted layer due to the coupling relationship between layers.To address this issue, a coordinated control strategy is proposed, which leverages MMC fast reactive power support and LCC non-fault layer over-trigger angle compensation. This strategy provides reactive power support to the LCC nonfault layer at the receiving end, depending on the levels of AC voltage drop. By considering the four-quadrant operation capability of the receiving-end MMC, reactive power support is supplied solely by the MMC when the required reactive power support falls within its four-quadrant operation range. The MMC reactive power support command value is determined by the voltage drop value of the common coupling bus. When the required reactive power support exceeds the MMC's four-quadrant operation range, the MMC reactive power support command value is set to the maximum reactive power value at the four-quadrant operation active power threshold, and the over-trigger angle compensation control for the LCC non-fault layer is simultaneously activated. Extensive simulation tests demonstrate that the proposed coordinated control strategy effectively suppresses simultaneous commutation failures in both high and low-end inverters.