UPt2Si2 has been long considered as a rare example of uranium intermetallic compound with strongly localized f-electrons which order antiferromagnetically below TN~35K. Recent high field and neutron scattering studies, however, suggests alternative view questioning the degree of localization in this system. Furthermore, our very recent synchrotron x-ray measurement on UPt2Si2 found that there is a superstructure with modulation wavevector ~ (0.4 0 0) below 320K. This wave vector is interesting in that it corresponds to the Fermi surface nesting wavevector found in URu2Si2 suggesting close relationship between this two seemingly different system. While the nesting give rise to the softening of magnon in URu2Si2, it is likely that the same instability leads structural modulation in our system. Here, we propose to study how the superstructural modulation does interplay with the magnetism at zero and high field by using high field magnet at EXED, HZB.