Abstract: The properties of expansive soil include water expansion, dehydration shrinkage, and cracking, with soil fissure having a significant impact on rainfall infiltration and runoff generation. This paper uses chestnut soil, which is frequently found in the Qinghai Lake Basin, as expansive soil, and performs an indoor rainfall infiltration runoff generation experiment with varying initial soil moisture contents for the soil shrinkage process. The goal of the experiment is to investigate the influence of the law of desiccation cracks of expansive soil on infiltration runoff generation, the effects of soil fissure and shrinkage on runoff intensity, cumulative infiltration rate, and moisture content under various initial moisture content conditions. The findings indicate that when the initial water content of the soil declined, soil shrinkage and fissure development increases, and all of the infiltration rates—initial infiltration amount, cumulative infiltration amount, initial infiltration rate, average infiltration rate, and stable infiltration rate—increase as well. The accumulated infiltration amount, fissure linear density, and soil surface fissure rate all exhibit strong correlations with correlation coefficients above 0.85. The more surface fissure area rate and linear density there are, the greater the impact of the fissure on infiltration. The longer the lag time between soil runoff generation and runoff generation from other sources, the smaller the runoff generation, and the longer it takes for the runoff intensity to stabilize, all are related to the degree of soil shrinkage and fissure development. Soil shrinkage and fissure are advantageous for the development of preferred flow. The capacity of the soil to supply water to deep soil increases with the degree of fissure formation. In order to complement the rainfall infiltration runoff generation law of expansive soil, the experiment investigates the influence of expansive soil shrinkage and fissure on infiltration runoff generation.