Objective To study the influence of intracapillary-transcapillary-interstitial unsteady coupling flow on the whole flow field and drug delivery in solid tumor. Methods Develop coupled fluid flow model. Intracapillary flow is governed by Navier-Stokes equations, transcapillary and interstitial fluid flow are described by Starling's law and Darcy's law respectively. Simulate the unsteady flow caused by step increase of capillary pressure and pulsating analytically and numerically. Results Relative to intracapillary, transport of pressure in the interstitium has hysteresis effect. The change of intracapillary flow will arise transient redistribution of interstitial fluid, and as a result, transcapillary pressure and interstitial pressure gradient will be increased. Conclusion Unsteady flow could increase transmural transport of drug and convective diffusion in tumor tissues as well.