The necessary and sufficient conditions of similarity of two idempotent matrices are proved, the idempotency of linear combinations of two idempotent matrices is discussed.

摘要证明了域上两个同阶幂等阵相似充要条件是它们有相同秩；给出了幂等阵相似标准型；讨论了两个幂等阵线性组合仍是幂等阵充要条件。