Abstract: Agricultural waste can be in the form of a liquid, slurry, or solid, such as manure, one of which the slurry is a mixture of urine, feces, washing water and disinfectant, containing complex components and many pathogenic bacteria. If the slurry was directly applied to farmland without any treatment, some severe negative effects can occur in this case. Firstly, the pathogenic bacteria in the slurry can be easy to enter the human body via the food chain, particularly harmful to human health. Secondly, the slurry contains a large amount of salt easy to cause crop "seedling burning", where ammonium salt is the main component of the salt in the slurry, mainly produced from the urine in the slurry to degrade the fecal organic matter. Finally, the degradation of organic matter in the slurry can make the soil in a temporary anoxic state, thereby to inhibit the growth of crops. At present, the general treatment to the slurry can be returning to the field after natural storage in most small and medium-scale livestock and poultry farms in China. Prior to directly returning to the field, the storage time of the slurry is usually only 1-2 months, particularly restricted by the sites. It is necessary to examine whether the stored slurry is suitable for returning to the field directly. The evolution of physical and chemical characteristics of the slurry after storage still remained unclear. Taking summer as the time node, while pig and cow manure water as the research objects, this paper aims to analyze the changes of fecal coliform, electric conductivity (EC) and chemical oxygen demand (COD) in the long-term storage of slurry, in order to obtain the optimum storage period and utilization mode of slurry. The results showed that the loss of ammonium nitrogen was more than 68% after six months of natural storage, indicating that it caused environmental pollution, and further reduced the nutrient value of slurry. A suggestion can be made to cover the surface of slurry with shelter or add acidification agent, in order to reduce the ammonia emission in slurry storage. After that, the slurry can basically meet the requirements of harmless after storage, but the pH value, EC Value and COD content of slurry were still high unsuitable to use directly. The high value of pH and EC indicated that there was a high concentration of ammonium salt in the slurry, and the long-term unreasonable application of fecal sewage can lead to soil salinization. Moreover, the application of slurry with high COD content can inhibit the root growth of paddy crops, thereby to affect root respiration, leading to the reduction in the yield of paddy crops, but it has little effect on dry land crops. Therefore, it is necessary to make a reasonable plan for the utilization of manure water before applying manure water to farmland, in order to reduce the risk of manure water when directly returning to farmland. In addition, a solid-liquid separation can effectively reduce the COD content and EC value in the slurry, thereby to promote the process of harmless slurry. The finding can provide a sound reference for the utilization of slurry resource and safe returning to the field.