The propagations of blast waves on Floating, Production, Storage, and Off-loading unit (FPSO) are influenced by the shapes, dimensions and arrangements of obstacles. In this paper, the effects of cylindrical obstacles on the characteristics of explosion pressures in the process modules of FPSO are studied by using computational fluid dynamic (CFD) method. Defining an effect coefficient η to express the changes of explosion pressures due to the existence of obstacles. It indicates that only the explosion pressures in the limited region adjacent obstacles can be affected by cylindrical obstacles. The increase of obstacle diameter only improve the η values front of the obstacles while increasing obstacle height can significant decrease the explosion pressures behind obstacle. When blast waves propagate multiple obstacles, the explosion pressures adjacent front obstacle are not affected by the rear obstacle, however, the explosion pressures in the gap of two obstacles are relieve due to the existence of front obstacle. The comparisons of effect of cubical and cylindrical obstacles reveal that cubical obstacles have more excellent pressure reduction ability as cylindrical obstacles can provide a larger pressure reduction region.