In order to improve the comprehensive knowledge on weak gel profile control effect, used are the micro etching model and parallel core physical model to conduct lab study on microscopic and macroscopic profile control and displacement mechanism of weak gel. Microscopic displacement experimental results shows that weak gel can enter large pore paths selectively, change liquid flow direction and conduct viscoelastic negative pressure oil absorption. Parallel core physics experiment results have verified the conclusion of microscopic displacement experiment from the macroscopic aspect. At the same time, due to characters of weak gel, the high permeability road is not blocked. Such conclusion can be obtained from migration process and morphological changes of weak gel in pore medium that main function of weak gel is displacement instead of profile control.