Abstract: This paper presents the principle of DT neutron yields diagnostic by copper activation and analyses the contributions of two kinds of nuclei 62Cu and 64Cu in the coincidence measurement. Two calibration methods of the diagnostic system are introduced for different ranges of neutron yields, which are the relative method and the 64Cu nuclei method. The scattered neutron of the accelerator room is measured by placing a polypropylene shield in front of a copper sample. The effect of the reaction 63Cu(n, )64Cu on the copper activation measurement is calculated and evaluated. This system is used to measure neutron yields from directly-driven implosions on Shenguang-Ⅲ laser facility. The experimental results show the relative method and the 64Cu nuclei method are fit in the range of DT neutron yield 109-1013 and 1012-1016, respectively. The effect of the scattered neutrons from the accelerator room on the calibrated sensitivity is about 0.4%, and the contribution of 63Cu capture reaction on the calibrated sensitivity using the 64Cu nuclei method is less than 1%. At present, DT neutron yields from directly-driven implosions on Shenguang-Ⅲ laser facility is about 81012.