To simplify the sequence control process, voltage source converter based high voltage direct current transmission system requires that VSC valve group has the ability to complete online entry process when direct current (DC) side is on the short-circuit condition. For this requirement, the key points of online entry for voltage source converter based high voltage direct current valve group based on hybrid MMC are described firstly. Secondly, the key strategies of valve group online entry are analyzed by the control characteristics and DC side equivalent circuit of hybrid MMC, and an implemental scheme based on DC modulation degree is proposed. On the short-circuit condition of DC side, control objectives can be realized including smooth converter deblock, fast DC current transfer, reliable bypass switch breaking and effective sub-module voltage balance. Finally, the effecs of valve group online entry strategies are verified by real-time digital simulations.