Abstract: Aiming at the issue of hardness reduction of some N type zinc-aluminium alloy after aging treatment, the zinc-aluminium alloy specimens were analyzed by hardness testing, chemical composition analysis, metallographic inspection, SEM analysis, EDS analysis, material heat treatment performance analysis and heat treatment verification testing. The results show that the N type zinc-aluminium alloy was developed on basis of the ZA50 type zinc-aluminium alloy series. The main reasons of hardness reduction after heat treatment were that the temperature of aging treatment was too high and the holding time of aging treatment was too long, causing the overaging phenomenon. At the end, some improving methods were suggested to meet the hardness requirement of the zinc-aluminium alloy.