Effects of groundwater depth on germination and seedling growth of Acorus calamus were studied by simulating experiment. The experimental barrels (diameter of 35.5cm and depth of 100cm) were filled with fluvial sands of 80cm depth. The water was introduced directly into the bottom of the barrels to build the groundwater depths in -60cm, -50cm, -40cm, -20cm and 0cm in different five barrels respectively. The same rhizomes of A. calamus were selected and planted in each barrel. The results were as follows: (1) Groundwater depth has significant effects on germination and seedling growth of A. Calamus. The plant can germinate in the groundwater depth from -60cm to -20cm, when groundwater depth decreased germination ratio reduced. On the 70th day, germination ratio of the -20cm treatment reached 90%, which were 2.25 and 3 times of those in the -50cm and -60cm treatments. Plant of 0cm treatment can not germinate. (2) Leaf length, width and area were positively correlated with groundwater depths and the significant correlations are able to be accepted (P < 0.01). With decreasing of groundwater depth, the number of the laminae reduces. The number of the laminae in -20cm and -40cm treatments were very significantly higher than those in -50cm and -60cm treatments (P < 0.01). Groundwater depth of -60cm was greatly affected on survival of plant seedling since plant seedling of -60cm treatment began to die after the 70th day. (3) With decreasing of groundwater depth, Chl.a, Chl.b and Car reduced but Chl.a/b increased. Plant leaves captured the light reducibly by the way of morphological adjustment and chlorophyll content reduction. (4) The laminae MDA and membrane permeability increased, which is led by low soil water content caused by low groundwater depth. (5)Groundwater depth has great effects on the rapid responded light-curves of A. Calamus. As groundwater depth decreases, the maximal photosynthetic electron transport rate (ETRmax) and the minimal saturated light intensity reduce, and the responded photoresponse capacity is weakened.