A series of soil bin experiment was carried out on sand to investigate if true model theory is applicable to blade-soil system and finally to find mathematical relationship between the dimensionless terms which contain the blade-soil parameters. The following conclusions were derived from the study. 1. It was proved that the draft of the prototype blade can be predicted without distortion by those of model blades with the length scale of 1.2, 2 and 2.4. 2. For the sand, bulk density was found to be a good measure of soil physical properties which are pertinent to predict the draft of the blade-soil system. 3. The mathematical relationship between $D/{gamma}W$ and d/W, ${eta}$, and $V^2/Wg$ are as follows ; $$frac{D}{{gamma}W^3}=124.98[frac{d}{W}]^2+7.16[frac{d}{W}]+0.43 \ frac{D}{{gamma}W^3}=-0.00099{eta}^2+0.13{eta}-2.01 \ frac{D}{{gamma}W^3}=0.041[frac{V^2}{Wg}]^2+0.08[frac{V^2}{Wg}]+1.3$$