A water pumping and injecting multi-layered concentric sphere neutron spectrometer includes a neutron detector, a plurality of shells concentrically provided, and a water pumping and injecting device; wherein an innermost shell surrounds a surface of the neutron detector; gaps are formed between adjacent shells for containing liquid; the shells are made of an aluminum material; a valve is arranged on each of the shells except the innermost shell; the water pumping and injecting device is connected to the valve of each of the shells except the innermost shell, so as to input water into the gaps or output the water from the gaps. Compared with conventional neutron spectrometer, weight of the water pumping and injecting multi-layered concentric sphere device and the neutron spectrum detection system of the present invention is greatly reduced, which is conducive to transportation and utilization. Meanwhile, combination of neutron spectrum data measurement and measurement data are increased.