Abstract: Qijiang Iron Mine's tailing pond is selected as an object to study the effect of capacity dilatation and saturation line increase on the stability of tailing pond.Safety factors of the orginal tailing pond and the tailing pond after enlarging capcacity under normal water level and flood level are calculated by using Sweden slicing method.As a result，the safety factor of the present tailing pond under normal water level and flood level are 1.90 and 1.63 respectively，which are all greater than 1.1 that is the minimum safety factor stipulated by the corresponding specifications.The safety factor under flood level decreases by 14.21%，compared to that under normal water level.Safety factor of tailing pond after enlarging capacity under two water levels are 1.27 and 1.17，so the enlarging results in the lower safety factor.It can be seen that the safety factor of tailing pond decreases with the increase of storage capacity and saturation line；however，the volume and radius of the sliding body increase largely.Although the safety factor of the tailing pond after enlarging capacity is still greater than the minimum safety factor，it has little emergency capacity.Thus，it is suggested that the saturation line of the tailing should be controlled after enlarging capacity，and the protective measures and monitoring management should be enhanced to avoid the happen of accidents after enlarging the capacity of tailing pond.

Key words: Tailing pond, Saturation line, Sweden slice method, Safety factor