Abstract: The γ-ray total absorption BaF₂ facility was used to measure the neutron capture reaction crosssection with high precision. An experimental neutron source condition of keV energy region was set up through the ⁷Li(p,n)⁷Be reaction, based on the HI-13 tandem accelerator providing the pulsed proton beam. By using the total absorption BaF₂ facility and online method, the prompt γ-ray cascades were detected when the neutron bombarded sample after shielding and collimation. Samples of Au, C, Nb and the blank were measured. The facility was checked and the online method for the (n,γ) reaction cross-section measurement was tested by comparing the deduced reaction cross-section ratio of ¹⁹⁷Au(n,γ)¹⁹⁸Au to ⁹³Nb(n,γ)⁹⁴Nb with the reference data. It also provides technical support for the implementation of (n, γ) reaction cross-section measurement at China Spallation Neutron Source (CSNS).