  In high-energy nuclear collisions, light nuclei can be regarded as a cluster of baryons and their yields are sensitive to the baryon density fluctuations. Thus, the production of light nuclei can be used to study the QCD phase transition, at which the baryon density fluctuation will be enhanced. The yield ratio of light nuclei, defined as $N(t)$$\times$$N(p)$/$N^2(d)$, is predicted to be sensitive observable to search for the 1st-order phase transition and/or QCD critical point in heavy-ion collisions. In this paper, we present the energy and centrality dependence of (anti)deuteron and triton production in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 7.7, 11.5, 14.5, 19.6, 27, 39, 54.4, 62.4, and 200 GeV measured by the STAR experiment at RHIC. We show beam-energy dependence for the coalescence parameter, $B_2(d)$ and $B_3(t)$, particle ratios, $d/p$, $t/p$, and $t/d$, and the yield ratio of $N(t)$$\times$$N(p)$/$N^2(d)$. More importantly, non-monotonic energy dependence is observed for the yield ratio, $N(t)$$\times$$N(p)$/$N^2(d)$, in 0-10\% central Au+Au collisions with a peak around 20-30 GeV. Their physics implications on QCD critical point search and change of the equation of state will be discussed. 
Light Nuclei ($d$, $t$) Production in Au + Au Collisions at   $\sqrt{s_{NN}}$ = 7.7 - 200 GeV