Water-based polyurethane (WPU) provides a number of benefits over typical solvent-based polyurethane. WPU ismore environmentally friendly, safe, and reliable. The WPU with polycaprolactone diol/polycarbonate diol (PCL/PCDL)complex soft segment was developed using a prepolymer technique to enhance the color depth of cotton knitted fabrics dyedwith reactive dyes. The appearance, particle size, zeta potential, and viscosity of WPU emulsions were analyzed. Thechemical structure, thermal stability, phase change performance, and topography of WPU films were characterized byFourier-transform infrared (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and atomicforce microscopy (AFM), respectively. The tensile and hydrophilic properties of the WPU films were examined by anelectronic universal testing machine and contact angle goniometer, respectively. The K/S value, rubbing fastness, washingfastness, and wearability of finished and unfinished dark cotton knitted fabrics were measured. Simultaneously, the chemicalstructure and morphology of fabrics were investigated using FTIR and scanning electron microscopy (SEM). The resultsshow the WPU-2 emulsion demonstrated excellent stability, and the WPU-2 film showed superior thermal stability. The K/Svalue of the dark cotton knitted fabric finished with WPU-2 emulsion (40 g/l) increased by 18.58 %, and the wet rubbingcolor fastness of the resulting fabric was enhanced. The SEM results show a layer of film covered the surface of the finishedfabric. In summary, the WPU can provide a new technique for enhancing the color depth of fabrics.