Preferential pathways in soil lead to nutrient leaching and groundwater contamination. However, the evolution of preferential flow with straw application remains uncertain. This study aims to experimentally determine the hypothesis that, depending on how it is applied, straw will either promote or inhibit the movement of soil preferential flow. Treatments with straw application rates of 0, 5, 10, and 15 t/ha and decomposition time points of 0, 60, and 240 d were set up for the potassium iodide–starch dye-tracer method. The results showed that the straw decomposition rate slowed down in the later stages. At 0 d, the preferential flow coefficients of straw application of 0, 5, 10, and 15 t/ha were 0.13, 0.14, 0.23, and 0.17, respectively. At 60 d, the preferential flow coefficients were approximately 0.17, 0.11, 0.22, and 0.12. Soil properties and irrigation quality improved at 0 d and 60 d. However, a marked increase of 0.31, 0.35, and 0.17 in the preferential flow coefficient was observed at 240 d. Soil properties and irrigation quality deteriorated at 240 d. These results indicate that the effect of straw incorporation and decomposition on preferential flow was initially inhibited and subsequently promoted. Soil properties and irrigation quality were initially improved and subsequently deteriorated. The study serves as a reference for rational utilization of agricultural residuals and scientific irrigation, suggesting that the optimal method of straw incorporation should be adopted based on the growth cycle of the crops.