Mangrove and acid sulphate soils developed from mangrove swamp are about 106,000 ha in China.One of the main characteristqcs of mangrove is the high S content in its chemical composition (generally 0.2%-0.6,0.4% on average,much higher than the 0.1% of tropic shrub).The characteristic greatly influences the genests and nature of the soils.When the remains of mangrove are buried and decomposed,a large amount of S enters the soil,making the kind of soil contain the buried mangrove layer with a high S content.In general,the surface soil is about 0.2% in the content of total S,and the buried mangrove layer is mostly over 0.3%,while other acid soils of tropic region are only about 0.04%.Besides,SO₄^2- content of the underground water in this kind of soil is 10-20 times as much as that of the sea waters of estuary.And it can also prove that S of the soil chiefly comes from the S of sea water accumulated by mangrove.After the swamp is enclosed and reclaimed,the soil water goes off.Sulphides produce a large amount of sulphate due to oxidization,so the soil reveals strong acidity-the lowest pH can reach 2.2,and lots of Al are activated and separated out.This is very harmful to the growth of plants.We consider the buried mangrove layer (the S-bearing horizon) as the diagnostic horizon (total S is 0.3% or higher; the pH of dried soil is 3.8 jarosite color value is ≥2.5 Y) and sub divide the soil into three types according to the appearing dep;h of the horizon: the shallow(<25cm),the middle (25-45cm) and the deep (45-70cm).