Within the frame of LDM (light dark matter)-model, the LDM exchange particle $U$-boson (with mass 10-100 MeV) can be produced from many meson decay process so it attracts a lot of attention. Considering the merit of searching the $U$-boson from $pi ^
{0}$ decay, the momentum spectra of light spin-1 vector $U$-boson from decay channel $pi ^{0}rightarrow gamma U$ and the energy spectra of positron decay from $Urightarrow e^{+}e^{-}$ at beam energy of 5-10 GeV are first presented by using a relativistic transport (ART) model. Moreover,the feasibility and rationality of searching the $U$-boson in the experiment at HIAF energy are discussed, which will be an important promotion to understand and ultimately detect the $U$-boson, both in theory and experiment.
