This paper deals with a parallel finite element analysis by Hierarchical Domain Decomposition Method (HDDM) of an electromagnetic field problem. The HDDM has been applied to the large-scale FEA of electromagnetics. In recent years, the electromagnetic field problems have been solved with 30 billion DOFs and 130 billion DOFs. However, since the problems involve symmetric systems with complex numbers and ill-conditioned systems, iterative methods often diverge. In this paper, improvement of convergence in the electromagnetic field analysis by HDDM will be considered.