Sludge adhesion on the inside wall of drying equipments may affect sludge drying performance. Effects of drying conditions on sludge adhesion were investigated by thermal drying experiments. It was found that sludge water content was the main important factor impacting sludge adhesion quantity. When sludge water content decreased with thermal drying, the adhesion quantity increased. The adhesion quantity reached the maximum value when sludge water content decreased to about 60%. The further drying reduced the adhesion quantity gradually. The heating temperature had almost no impact on sludge adhesion when the heating temperature was no higher than 120℃, while the adhesion quantity increased with the increasing heating temperature when the heating temperature was higher than 120℃. Conduction heating would lead to more sludge adhesion compared with convection heating. Rough heating interface would also help sludge adhesion.