In this paper, we establish the uniqueness of heat flow of harmonic maps into (N, h) that have sufficiently small renormalized energies, provided that N is either a unit sphere \(S^{k-1}\) or a compact Riemannian homogeneous manifold without boundary. For such a class of solutions, we also establish the convexity property of the Dirichlet energy for \(t\ge t_0>0\) and the unique limit property at time infi?nity. As a corollary, the uniqueness is shown for heat flow of harmonic maps into any compact Riemannian manifold N without boundary whose gradients belong to \(L^q_t L^l_x\) for \(q>2\) and \(l>n\) satisfying the Serrin's condition.