【Objective】In recent years, disastrous soil pollution incidents have been taking place quite frequently. Surface activating agents were widely used in remediation of polluted soils as it is an effective soil amendment. Addition of surfactants can accelerate remediation processes and improve soil properties, and alter the surface tension of pore water in the soil as well. It has been demonstrated in a number of studies that surface tension of pore water is substantially reduced by adding a small amount of surfactant, and altered, too, by adding some organic compounds, which are often found as residues in wastewater treated and recycled as irrigation water. The three major equations describing characteristic of the interface, i.e. Young equation, Laplace equation and Kelvin equation, are all related to surface tension. So gas-liquid interfacial tension (also surface tension) is the main factor affecting shrinkage cracking of soil, and besides, changes in surface tension are bound to have an important impact on soil-water characteristics of soil. In addition, under actual climate conditions and natural environment, which are often very complicated, soils are generally subjected to several times of drying and wetting alternations, which may cause delay of the soil water characteristic curve, and variation of contact angle is also an important factors causing delay of the curve, while contact angle and surface tension are closely related to each other. It is, therefore, of great theoretical and practical significance to characterize soil shrinkage cracking from the view point of surface tension as affected by wetting and drying alternation to agricultural irrigation as well as environmental protection.【Method】In order to better understand the effect of surface tension on soil shrinkage cracking, an experiment designed to have the soil samples subjected to wetting-drying alternations was carried out, with drying temperature set at 25°C and 60°C.The experiment had three groups of soil samples treated with different solutions, thus being different in surface tension when initially saturated. Changes in soil water content and evolution of surface cracks were monitored in the samples under dehumidification, and even photos were taken for quantitative analysis of fissure development degree (δ) on the surface of the samples using the digital image processing technique. Then comparative analysis was done for relationships of surface tension with δ and changes in water content, and with temporal variation of δ.【Result】Results show that with the drying-wetting alternation going up in frequency, δ of the soil at the end of the experiment increases somewhat, but not large in magnitude; δ is significantly influenced by temperature: the higher the temperature, the earlier the initial fissures appear. When the drying temperature rises from 25°C and 60°C, critical water content at the onset of cracking increases from 38% to 41%, and δ of the soil at the end of the experiment by 20%～40%; when the drying temperature remains the same, with declining surface tension soil fissure development slows down and δ of the soil at the end of the experiment lowered; but it is found that δ of the soils low in surface tension may be higher than that of the soils high in surface tension at the initial stage; when water content is the same, the higher the surface tension, the more the fissure development degree. Regardless of temperature environment, in terms of surface tension and fissure development degree, the three groups of soil samples exhibits an order of samples treated with pure water >samples treated with alcohol solution >samples treated with soap water.【Conclusion】In a word, wetting-drying alternation does have certain influence on development of soil fissures; and temperature is a major faction directly controlling shrinkage cracking of soil; While surface tension is one restraining the processes.