By means of ultra-violet (UV) irradiation with photoinitiator and multifunctional crosslinking agent, the crosslinking modification of ultrahigh molecular weight polyethylene (UHMWPE) fibers prepared by gel spinning was performed. Thermal and mechanical properties of fiber samples were examined using differential scanning calorimeter, thermomechanical analysis apparatus and tensile tester, the gel content of fibers was measured by a standard device, the fiber surface was examined by scanning electron microscope. The results indicate that the optimal irradiation time is I to 2 hours. The modified fiber can then preserve its original mechanical properties, or may have better behavior, meanwhile, such fibers have improved heat- and creep-resistant behaviors.