To solve the problem that the traditional "narrow-band,far-field" resolution formulas are no longer suitable for Impulse Radio Ultra-Wide Band(IR-UWB) real aperture imaging systems,a new algorithm to compute the resolution was proposed.On analysis of IR-UWB near-field imaging principle,the formulation of resolution in down-and cross-range for single antenna was derived.Combined with signal superposition in the process of imaging,an algorithm to compute the resolution for real-aperture uniform linear array was presented.Numerical simulation results of ideal point targets imaging verified the correctness of the algorithm.