Abstract: The sand-carrying capacity of fiber fracturing fluid largely depends on its rheological property and microstructure. For the purpose of further understanding the sand-carrying mechanism of fiber fracturing fluid, fiber dispersion was observed and rheological property of fiber-guar gum base fluid was studied through laboratory tests, and the microstructure of fiber-guar gum base fluid was studied through scanning electron microscope (SEM). The research result shows: fiber is evenly dispersed in guar gum base fluid; fiber-guar gum base fluid is conforming to rheological model of power law; fiber can improve the viscosity and enlarge the structural strength and internal friction of guar gum base fluid effectively; at 20 ℃, 0.4% fiber dosage can increase the viscosity of guar gum base fluid to 129.009 mPa·s from 32.496 mPa·s, and even if the temperature rises, viscosity and structural strength of guar gum base fluid can still be kept high; fiber-guar gum base fluid can form a reticular structure and enhance the bounding and carrying capacity to proppant. Moreover, the research result can be used as a reference for the follow-up theoretical research and field application.