The mechnical analysis was made to two types of structure modelsof oblique and plane seams pitched with rectangular slab stones, in regard to the condi-tions of waves and water flows, thus the basic mechanical equilibrium relationship ofcritical stability of stones was obtained. On the basis of 40 varied structure sectionmodels and 1,380 times of wave model test was then made non-dimension analysis ofrelevant factors which may affact the thickness of pitched stones. As a result, thecalculation formula for determing the thickness of building pitching stones were putforward, which may provide a theoretical framework for engineering design of break-waters. Besides, some experimental results about the standard for breakwater design aswell as some analytic ideas were also provided in this paper.