An on-line monitoring system of neutron fluence was established based on the understanding of the linear relationship between Δ1/β of transistor and neutron fluence. The hardware of this system consisted of computer，GPIB bus unit, matrix switch, function waveform generator and digital oscilloscope; while the software was built up by Labview program. The calibration tests were performed at the Xi'an TRIGA reactor. This system actualized an on-line test of neutron fluence in the radiation cavity. The equivalent damage coefficient of XAPR and CFBR-Ⅱ was obtained by using this test system.