The in-plane and out-of-plane emission of unstable light nuclei was measured in the reaction of ４０Ａｒ＋１９７Ａｕ at energy 25MeV/u by means of extensive particle-particle correlation. An in-plane enhancement is observed for mid-rapidity unstable light nuclei, indicating a rotational effect exists in this reaction system. This in-plane enhanced emission becomes stronger with increasing of impact parameter, but becomes a little weaker with increasiong of energy of the excited state.