This work aimed to study the UV-curable waterborne polyurethane emulsion with adjustable double bond content and its film properties. The pentaerythritol diacrylate (PEDA) was prepared via direct esterification, and used as a functional chain extender to synthesize a series of UV-curing waterborne polyurethane emulsion by introducing the C＝C bond into the side chain, with 2,4-tolylene diisocyanate (TDI), polyethylene glycol (POL-756T), dimethylol propinic acid (DMPA) as main materials. The effects of different PEDA and DMPA contents on the emulsion and film properties were studied. The increase of PEDA content could lead to the increase of film tensile strength and thermal stability while the decrease of elongation at break. The increase of DMPA content could lead to improved storage stability, increased transparence, finer particle size and decreased water resistance. When the PEDA content was 6.1% and the DMPA content was 8.3%, the WPU emulsion had good appearance and stability, and the coating film had excellent water resistance and mechanical property.