Abstract: This paper introduces the principles, instrumentation, implementation and industrial applications of an on-line thermal neutron promptgamma activation analysis system (using a ~(252)Cf neutron source, AmBe neutron source, or neutron generator). The energy resolution of the system at the H prompt-gamma full-energy photopeak is 3.6keV. The concentration measurement error of A1_2O_3, Fe_2O_3, CaO, SiO_2, Na_2O, TiO, and H_20 is ±0.3％, ±0.1％, ±0.3％, ±0.3％, ±0.2％, ±0.2％and ±0.5％ respectively. The system has been tested on-site at both the Shandong and the Zhengzhou Aluminium Works. Our preliminary on-site measurements confirm that the stability, reliability, measurement range and accuracy of the system can meet the requirements of the aluminium production process. Facilitation of this system at aluminium plants is expected to produce much higher economic benefits by reducing the plant costs through reduced energy consumption, more rapid qualification of pulps being mixed during the production process, and in reduced labor costs.