Design/methodology/approach The Reynolds equation was solved using the finite difference method. A study was carried out on the effects of groove bottom surface roughness, rotational speed, pressure, eccentricity ratio and groove depth difference on the sealing performance of a cylindrical gas film seal. The differences in sealing performance such as load capacity, leakage, ratio of load capacity to leakage and friction power of equal depth groove, ladder-like groove and sloped bottom groove were comparatively analyzed. Findings Within the scope of this study, the groove bottom surface roughness has less influence on the sealing performance. The sealing performances of the ladder-like groove and sloped bottom groove are relatively similar. The load capacity of both axial divergent unequal depth grooves and circumferential convergent unequal depth grooves is larger than that of equal depth grooves. However, the comprehensive sealing performance of the axial divergent unequal depth groove is the most optimal. Originality/value The equivalent problem of groove depth between unequal depth grooves and equal depth grooves was treated using the equal gas film volume method. The effect of groove bottom surface roughness on the performance of cylindrical gas film seal was investigated. The sealing performances of the equal depth groove, sloped bottom groove and ladder-like groove under different rotational speeds, pressures, eccentricity ratios and groove depth differences were investigated, and the differences in their sealing performances were comparatively analyzed. This provides a certain reference for the theoretical research and design of cylindrical unequal depth groove gas film seal. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2024-0316/