I will investigate UV completion of Higgs inflation in the Palatini formalism. It is known that the cutoff scales for the perturbative unitarity become much smaller than the Planck scale to be consistent with CMB observations. Expecting that the low cutoff scales originate in the curvature of a field-space spanned by the Higgs fields, I consider embedding the curved field-space into a higher dimensional flat space and apply this procedure to the Palatini-Higgs scenario. I will show that, while the new field introduced in this way successfully flattens the field-space, the new field can not uplift the cutoff up to the Planck scale. I will also compare the result with vanilla Higgs inflation.