The ferromagnetic core of power transformer is susceptible to dc bias and has special nonlinear and hysteretic characteristics under dc-biased magnetization. The dc-biasing magnetization curve of a square laminated core (SLC) can be obtained by dc bias test. The harmonic- balanced finite-element method (HBFEM) combined with the fixed-point technique is used to calculate the dc-biasing magnetic field in the SLC based on the measured dc-biasing magnetization curve. A locally convergent method in harmonic domain is presented to determine the fixed-point reluctivity, which can speed up the convergence of harmonic solution. The dc-biasing magnetic fields are computed by using the basic and dc-biasing magnetization curves respectively. The results indicate the dc-biasing magnetization curve is more reasonable than the basic one in the analysis.