The effect of elevated temperature and magnetic field on recorded magnetization structure of a perpendicular magnetic recording HDD medium has been studied by in-situ magnetic force microscopy (MFM). The recorded bit shape started to change in the track and the cross-track directions when heated at 200°C. When a magnetic field was applied at elevated temperatures, variation of recorded magnetization was enhanced compared with the case with only heating. A quantitative analysis of magnetization structure variation under an influence of heat and magnetic field is carried out by taking the difference of MFM images observed for a same area under different environmental conditions.