A new multi-exponential inversion method for NMR relaxation signals is presented and tested, which is based on differential evolution (DE) algorithm. The inversion of T2 spectrum in NMR is reduced to a non-negative constraint optimization problem, and solved directly by DE algorithm without pre-assigning the distribution of relaxation time T2. The validity and effectiveness of our method is demonstrated by computer simulations and the inversion of practical NMR data under low SNR.