Abstract: The Baihetan-Jiangsu ±800 kV UHV DC transmission project, which will be put into operation on July 1, 2022, is the world's first creative development and application of a new technical solution for UHV hybrid cascaded DC power transmission. In this paper, a subsequent phase commutation failure prediction with a certain time margin is carried out for the inverter side line commutated converter (LCC) based on this system background. The control role of the LCC controller on the electrical quantities and the voltage support role of the modular multilevel converter (MMC) on the LCC are analyzed, and the mechanism of subsequent phase commutation failures of the inverter-side LCC of the hybrid cascaded DC transmission system is clarified. The relationship is derived between the shutdown angle at the end of the recovery process of the inverter-side LCC after the first phase commutation failure and the minimum value of the line transmission power after the fault, and the concept of threshold power is defined. Then the quantitative relationship between the turn-off angle and the threshold power is established, and a subsequent phase commutation failure prediction method is proposed for comparing the minimum value of the DC transmission power after the fault with the power threshold. Finally, the corresponding simulation model is built in the PSCAD/EMTDC to verify the accuracy of the theoretical analysis and the prediction method.