The invention discloses a high-sensitive environment neutron spectrum analysis system for a small block heap, being suitable for the energy spectrum, fluence, and dosage on-line measurement of the surrounding environment of a small fast neutron reactor and preventing the mutual interference caused by the detector scattered layout. The system includes a neutron probe, an electronic system and an energy spectrum analysis system; the neutron probe is composed of a plurality of detection units, each detection unit includes a thermal neutron sensitive detector and a moderator that is wrapped outside the detector, parts of the detection units are built-in and embedded in the proliferation layers of the moderators; the moderators of different detection units are different in thickness, the detection units are uniformly distributed around the small block heap, the center lines of the detection units are radially vertical to the small block heap, the detection units simultaneously perform signal detection, the detected signals are transmitted to the energy spectrum analysis system after being processed by the electronic system.