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

摘证明了数域上两个同阶幂等阵的充条件是它们有同的秩；给出了幂等阵的准型；讨论了两个幂等阵的线性组合仍是幂等阵的充条件。