Irrigation and rainfall would make tilled loss soil relatively compact because water makes soil particles cohered to each other, altering the soil structure and erosion resistance. Soil disintegration rate is regarded as a key parameter to evaluating soil’s erodibility. Accurate prediction of disintegration rate of tilled soil is very important to effective management and conservation of soil and water. In this paper, simulation of wet-dry alternation of soil was performed using a soil box to explore effects of the alternation on soil bulk density and soil hydrostatic disintegration rate, and the effect was simulated with the Richards model. Soil wetting process was simulated by immersing the soil in slack water and soil drying process was by oven-drying. The two processes went one after the other forming a round of wet-dry alternation. After the alternation, the soil gradually concreted. Based on soil concretion settling rate and quantity of the soil sample, soil bulk density was calculated. At the same time soil samples were collected with a square ring sampler for determination of soil disintegration rate using the hydrostatic disintegrating method. The soil samples used in the experiment were collected from the topsoil layer of a farmland in Yangling and silt loam in soil texture. The Richards model is a monotone increasing function extensively used to describe growth process. In describing the growth process, the model has two peak values of growth variation rate, which are the two division points of the growth process. However, the cumulative soil disintegration process presents a typical S-curve, so the Richards model can be used to simulate the soil disintegration process and to analyze effect of wet-dry alternation on soil disintegration rate. The paper has come mainly to the following conclusions: With the wet-dry alternation increasing in frequency, bulk density of the soil gradually becomes heavy, but concretion slows down, and disintegration rate declines steadily. The Richards equation can be used to better describe the process of soil disintegration. Based on the characteristic points of soil disintegration displayed in the model, soil disintegration process can be accurately divided into three phases: slow disintegration phase, exponential disintegration phase and disintegration completion. With rising alternation frequency, the slow disintegration phase extends, delaying the exponential disintegration phase, and disintegration rate declines. Especially after three rounds of wet-dry alternation, soil disintegration rate reduces significantly and soil erosion resistance improves. Having experienced wet-dry alternation, soils are much lower in disintegration rate during their soil exponential disintegration phase, of which the proportions to the total are also significantly lowered. After one or two round of alternation, soil disintegration in the exponential disintegration phase accounts for 60% of the total, but after the third round, soil disintegration in that phase accounts only for 29% of the total. Obviously. wet-dry alternation can effectively reduce soil disintegration rate and improve erosion resistance of soil.