The invention relates to a method for determining content of guar gum or modified derivatives thereof and determining adsorption quantity of guar gum or modified derivatives thereof in a stratum. The method comprises the following steps: preparing a standard solution of guar gum or modified derivatives thereof, drawing a content-absorbance standard curve, and determining the content of the guar gum or modified derivatives thereof by an absorbance process. When the method is used for assay determination of the adsorption quantity of the guar gum or modified derivatives thereof in the oilfield stratum, the contents of the guar gum or modified derivative thereof in the guar gum or guar gum modified derivative solution for oilfield fracturing fluids before and after adding rock solid particles are respectively determined, and the difference between the contents is the adsorption quantity of the guar gum or modified derivatives thereof in the rock. The method is simple to operate, and has accurate determination results.