A preliminary study of the statistical estimation of the quadratic frequency response function (QFRF) using higher order spectral analysis is carried out and compared with an analytical QFRF. The QFRF is estimated via digital higher-order spectral analysis from simulation data of sea wave elevation and slow sway drift wave force on a ship in a unidirectional random sea. The initial result shows that the two QFRF's are in good agreement in the difference-interaction region where in good agreement in the difference-interaction region where the slow drift force dominates. The estimated QFRF is able to "predict" the simulation drift force within 1% mean square error.