The invention provides a solvent-free waterborne polyurethane dispersion, a preparation method and application thereof. The preparation method comprises the steps of: (1) preheating the polymer diol,diisocyanate, small molecular diol, a low melting-point dihydroxy-terminated "Y" type side chain hydrophilic chain extender and a catalyst respectively, and inputting the materials into a double-screwreactor for reaction so as to obtain a polyurethane melt; (2) injecting the polyurethane melt into a shear pump, and simultaneously injecting water with a surfactant into a shear pump for shearing dispersion; and (3) performing cooling and pressure reduction, and conducting stirring to obtain the solvent-free waterborne polyurethane dispersion. The method provided by the invention solves the technical problems of synthesis, dispersion, emulsification and the like of high viscosity waterborne polyurethane melt, improves the production efficiency and batch stability of products, and has no needof an expensive hydrophilic chain extender. The solvent-free waterborne polyurethane dispersion can be applied to synthetic leather, adhesives, paint, fabric coatings, finishing agents, base cloth priming resin, surface resin, bonding layer resin, interlayer resin or foaming layer resin.