Two-dimensional metal carbide (MXene), represented by titanium bicarbonide (Ti3C2TX), has great application potentials in the field of electromagnetic wave absorbing materials due to its excellent dielectric properties. However, its high conductivity and single dielectric loss mechanism limit the further improvement of its microwave absorption performance. Waterborne polyurethane (WPU) has been widely used in various fields due to its advantages of environmental protection and excellent mechanical properties. Therefore, the magnetic nickel particle modified MXene absorber (Ni@MXene) was prepared by solvothermal method in this paper. The purpose is to improve the matching characteristics of MXene and introduce magnetic loss mechanism, thereby improving the wave-absorbing performance of MXene. Three kinds of Ni@MXene with different nickel contents were prepared by adjusting the mass ratio of nickel ion to MXene. The results show that the introduction of nickel can effectively improve the matching characteristics of MXene and significantly enhance the wave-absorbing properties of MXene. The Ni@MXene/paraffin composite has the minimum reflection loss (RL) of -32.07 dB(at the frequency of 11.90 GHz) and the effective absorption bandwidth (EAB) can reach 2.63 GHz (ranging from 11.70 GHz to 14.33 GHz) with a filler mass fraction of 40% and thickness of only 1.7 mm. Finally, the composite with the mass fraction of 20% was prepared by using MXene and Ni@MXene as filler and WPU as matrix, which further verifies the improvement of absorption performance of MXene by the nickelization modification.