Nowadays, the technology of the receiving end under hierarchical connection mode is widely adopted in the UHVDC project.With the affection of hierarchical connection mode, high and low-end reactive power is controlled respectively and core controller is put down to the valve group layer.How to optimize the mode of online valve group deblock and making it apply ripely into hierarchical connection mode should be explored urgently.This paper introduces the control strategy of online valve group deblock under hierarchical connection mode in detail, and points out the relationship between controller switch and trigger angle change in the process of online input.By comparing with the conventional one, it puts forward the new features of online valve group deblock strategy under hierarchical connection mode.It also indicates the key steps of online valve group deblock through the actual modeling and test support.The field test results show that the control strategy described in this paper is applicable to the existing UHVDC project under hierarchical connection mode, and the inverter station under hierarchical connection mode should open the BPS switch in a reasonable time interval to ensure the reliable operation of the valve group.