This paper studies the reachability and the structure of reachable semigroup of bilinear control systems on Lie group. In the second section some equivalency lemmas are given, which not only simplify the proofs of the main results, but discover some properties of systems also. In the third section some conditions are advanced that the reachable semigroup of system is weakly symmetric by means of the study of one prameter subgroups. This study is discussed by manifold theory and matrix theory, respectively. In the last seetion, some topological properties of the reachable semigroup are advanced.