The length-to-breadth ratio ( L/ B) of a heavy icebreaker is generally between 4~5. The applicability of conventional calculation formulae for calculating wave loads on hull girder is limited. The characteristics of heavy icebreakers hull lines differ significantly from those of vessels designed for open waters. Numerical methods are consequently required to study the characteristics of wave loads on hull girder. A time-domain Rankine source method accounting for speed is employed to predict the wave loads on hull girder by using the hydrodynamic software WASIM. Both the long-term values of linear wave loads and the direct calculation results of nonlinear wave loads are obtained. Comparisons are then made among the long-term linear wave loads (after nonlinear correction), the directly calculated nonlinear wave loads and the standard values. The results show that the long-term linear vertical wave bending moment is approximately 1.4 times the standard linear value, and the long-term linear vertical wave shear force is 1.9 times that of the standard linear values, owing to the unique hull lines of heavy icebreakers. It is indicated that the standard formulae cannot provide a reasonable evaluation of the wave loads on the hull girder for these vessels. From a practical engineering design perspective, the long-term linear vertical wave loads (after non-linear correction) at a speed of 5 knots are adopted as the design wave loads of the hull girder for the evaluation of the overall strength of the hull structure. The non-linear effect of the sagging wave bending moment is significant, resulting in special consideration of the structural buckling of long superstructures during the check of the longitudinal strength of the hull under sagging condition.