The present application relates to a detection structure for fast neutrons and a method for acquiring a neutron energy spectrum, the detection structure for fast neutrons comprises seven semiconductor detection units and a conversion layer made of a hydrogen-containing material, the seven semiconductor detection units comprise a first, a second, a third, a fourth, a fifth, a sixth and a seventh semiconductor detection unit arranged sequentially, the first, the fourth and the seventh semiconductor detection unit constitute an anticoincidence detection group, the second and the third semiconductor detection unit constitute a neutral particle background detection group, the fifth and the sixth semiconductor detection unit constitute a recoil proton detection group, the conversion layer is disposed between the fourth and the fifth semiconductor detection unit, incident neutrons collision with hydrogen atomic nuclei and generate the recoil protons. The present application can effectively reduce influence of background signals on the measurement and improve accuracy of the inversed neutron energy spectrum.