The　investigation　of　magic　numbers　for　nuclei　in　the　hyperheavy　region　(Z＞120)　is　an　interesting　topic.　The　neutron　magic　number　N=350　is　carefully　validated　by　the　deformed　relativistic　Hartree-Bogoliubov　theory　in　continuum　(DRHBc),　via　analysing　even-even　nuclei　around　N=350　of　the　Z=136　isotopes　in　detail.　Nuclei　with　Z=136　and　340　＜=　N　＜=　360　are　all　found　to　be　spherical　in　their　ground　states.　A　big　drop　of　the　two-neutron　separation　energy　S2n　is　observed　from　N=350　to　N=352　in　the　isotopic　chain　of　Z=136,　and　a　peak　of　the　two-neutron　gap　delta　2n　appears　at　N=350.　There　exists　a　big　shell　gap　above　N=350　around　the　spherical　regions　of　single-neutron　levels　for　nucleus　with　(Z=136,N=350).　These　evidences　from　the　DRHBc　theory　support　N=350　to　be　a　neutron　magic　number　in　the　hyperheavy　region.