Field study on the ecology and reproductive biology of S. sinensis was conducted from May 2009 to March 2011 in the rice paddy-fields in Thanh Hoa province. the authors recorded eight types of crab holes, with round or eliptic entrances and the depths from 28 to 82mm. S. sinensis is diurnal and nocturnal but more active at night time. This species is affected by air temperature and humidity. Temperature and humidity affect to the crab's action and the humidity is above 74.90 percent is suitable for this crab species. S. sinensis is omnivorous. This crab eat during the day and at night time. The prey items comprise plant, shrimps, aquatic insects, shellfishes, humus, and the organic residue. The breeding season of S. sinensis is from March to November, but mainly in April-May and September-October.