In this paper, we consider the preconditioned iteration methods for ill-conditioned BEM linear system. We propose a class of generalized refined preconditioners and study some relevant properties of these preconditioners, as well as the computational complexities in application. If A is the coefficient matrix of the BEM linear system and M0=A0−1 is a basic preconditioner obtained from the incomplete LU factorization of A, the proposed preconditioners are mainly applicable to the system that M0(A−A0) tends to have a small portion of singular values greater than 1. Finally, we present several numerical examples to show the effectiveness of the proposed preconditioners.