Objective To study the flow property in microcirculation and material exchange. Methods Based on the porosity concept used in the petroleum fields, this paper set up the double porosity medium model of capillary and tissue. In the case of regardless the liquid permeable pressure of capillary and tissue , the leakage formula is obtained. The numercal analysis was conducted under different conditions; with the affection of time and without the affection of time. Results The comparison of numerical results show that: the leakage volume decreased along capillary without the affection of time; with the affection of time the leakage volume increased quickly at first and the decreased slowly. Conclusion The results are benefits to further study of material and energy exchange in the system of capillary and tissue.