The effect of a three-dimensional head field on the writing process in longitudinal recording was investigated by micromagnetic simulation. The calculated media coercivity and write bubble clearly showed field angle dependence. The dibit and overwrite calculated at different field values indicated that the out-of-plane field component significantly reduced the required minimal in-plane field in the write process. In addition, the Williams-Comstock model was modified to include the effect of the out-of-plane field component. The results also predicted a reduced optimal in-plane field and agreed reasonably well with the micromagnetic simulation.