By incorporating glycerol monostearate (GMS) into the main chain of waterborne polyurethane (WPU), a comb-like branched structure was successfully constructed, leading to the synthesis of a series of WPU dispersions with varying GMS contents. The influence of GMS content variation on the shear-thinning resistance and film properties of WPU dispersions was systematically investigated. Rheological analysis revealed that at low shear rates, the comb-like branched modified samples exhibited enhanced resistance to shear thinning. At high shear rates, the formation of transient network structures among internal polymer chains strengthened the particles’ ability to resist deformation, coupled with an increase in dispersion particle size, which synergistically contributed to maintaining a certain level of shear-thinning resistance in the WPU dispersions. Film property tests demonstrated that when the ratio of N210 (polyether polyol) to GMS was 9:1 (N9G1 film), its elongation at break remained around 820% while the tensile strength reached 17.1 MPa, indicating a significant overall improvement in mechanical properties. Comb-like branched waterborne polyurethane provides a novel approach to regulating the rheological properties, with potential applications in coatings, inks, cosmetics, and related fields.