A condition survey was conducted to investigate surface condition of pavement on steel plate deck of bridge. The results of the survey showed that main distress mode of the pavement are longitudinal cracks which occur at web of longitudinal rib as well as at the position between the webs. To make clear the causes of the crack, we performed strain analysis using overlaid FSM. The strain analysis indicated that, although large tensile strains appeared in the pavement at the web of rib, the strains between the webs were basically compressive. These results can not explain the cracks between the webs. Laboratory experiment modeling the pavement on plate deck was conducted and the results indicated the possibility of occurrence of the cracks by repetition of compressive strain.