Representations for the generalized Drazin inverse of an operator matrix A B C D are presented in terms of A, B, C, D and the generalized Drazin inverses of A, D, under the condition that BD d = 0, and BD i C = 0, for any nonnegative integer i. Using the representation, we give a new additive result of the generalized Drazin inverse for two bounded linear operators P, Q ∈ B(X) with P Q d = 0 and P Q i P = 0, for any integer i ≥ 1. As corollaries, several well-known results are generalized.