A self-adaptive differential evolution neutron spectrum unfolding algorithm (SDENUA) is established in this study to unfold the neutron spectra obtained from a water-pumping-injection multilayered concentric sphere neutron spectrometer (WMNS). Specifically, the neutron fluence bounds are estimated to accelerate the algorithm convergence, and the minimum error between the optimal solution and input neutron counts with relative uncertain-ties is limited to 10–6 to avoid unnecessary calculations. Furthermore, the crossover probability and scaling factor are self-adaptively controlled. FLUKA Monte Carlo is used to simulate the readings of the WMNS under (1) a spec-trum of Cf-252 and (2) its spectrum after being moderated, (3) a spectrum used for boron neutron capture therapy, and (4) a reactor spectrum. Subsequently, the measured neutron counts are unfolded using the SDENUA. The uncertainties of the measured neutron count and the response matrix are considered in the SDENUA, which does not require com-plex parameter tuning or an a priori default spectrum. Theresults indicate that the solutions of the SDENUA agree better with the IAEA spectra than those of MAXED and GRAVEL in UMG 3.1, and the errors of the final results calculated using the SDENUA are less than 12％. The established SDENUA can be used to unfold spectra from the WMNS.