This paper reports the rapid in-situ calibration of neutron flux monitors completed on the HL-3 tokamak device, a process that took only 14 h. The efficiency of the detection system, consisting of B-10 proportional counters and U-235 fission chambers, was determined at 33 positions using a Cf-252 source (8.29 × 106 n s−1). The Campbell model for high-flux measurements was cross-calibrated using plasma neutrons. This calibration system achieves a measurement range from 1010 n s−1 to 1017 n s−1 with a time resolution of 10 ms and an uncertainty less than 20%. The successful implementation of this efficient calibration activity, from process design to cross-validation, provides a viable reference strategy for planning neutron diagnostic systems for International Thermonuclear Experimental Reactor and other future fusion reactors.