The inverters of ultra-high-voltage direct-current（UHVDC） hierarchical connection system have electrical coupling relationship on both the AC and DC sides. When the fault occurs in one of the two voltage level AC systems

the drop of AC voltage will cause inverter valves commutation failure in the fault layer

and the increase of DC current also renders the inverter valves in non-faulty layer to have the risk of commutation failure. The start-up time of existing commutation failure prevention（CFPREV） of non-fault layer is later than that of the fault layer

which can not effectively prevent the commutation failures of inverter valves in non-fault layer. In order to solve the problem

we propose a commutation failure suppression strategy based on multi-criteria prediction in UHVDC hierarchical connection system

which combines the commutation current-time area with the original CFPREV

so that the start-up time of CFPREV in non-fault layer is advanced

and the acting accuracy is increased

improving the suppression effect of commutation failure of the inverter valves in non-fault layer effectively. A simulation example of UHVDC hierarchical connection system is built on the PSCAD/EMTDC

and the simulation results verify the effectiveness of the proposed suppression strategy.