Abstract: Interstitial fluid is the surroundings that cells livein. Spatial distribution of protein in interstitial space is not uniform.This article is to numerically investigate the interstitial fluid ininterosseous membrane of lower limb based on a new view of Straling'shypothesis and to study the effect of unequal distribution of protein in theinterstitial fluid. The results showed these parallel capillaries could leadto directional flow of interstitial fluid under the equal and unequalprotein distribution conditions. The fiber matrix in the capillary wallopposed protein filtration induced the unequal distribution of protein. Thehigh pressure in the capillary near the artery prevented protein fromdiffusing to the capillary wall to induce the lower protein concentration.Furthermore, the unequal spatial distribution of protein in interstitialspace had a strong influence on the interstitial fluid flow. The numericalresults in the present work were in good agreement with the experimentaldata from Weinbaum.