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 δ2n 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.