The event-event coincidence spectroscopy system was successfully established and operated on thermal neutron beam of channel N0. 3 at Dalat Nuclear Research Reactor (DNRR) with resolving time value of about 10 ns. The studies on level density, gamma strength function and decay scheme of intermediate-mass and heavy nuclei have been performed on this system. The achieved results are opening a new research of nuclear structure based on (n, 2ɣ) reaction.