In order to explore the effect of straw mulching on the preferential flow paths of paddy field in the Karst area of northern Guangxi, the method of field staining and tracer, combined with image morphological analysis and spatial statistical analysis are used to study the priority path and spatial distribution characteristics of straw mulching and non-mulching paddy fields in north karst area of Guangxi. The result show that with the increase of soil depth, the soil staining morphology of paddy fields under the condition of straw mulching is changes from surface scattered distribution to deep dyeing form crumb scattered distribution. However, the staining morphology mainly changes from cluster dendritic fissures to lumpy distribution on both sides of the non-straw mulching conditions in the paddy field, and the average total dyeing area ratio of straw mulching paddy field (18.23%) is only 0.75 times higher than the non-cover conditions paddy field with significant difference (P <0.05).The average total number of preferential flow paths of straw mulching (6323) is only 0.81 times higher than that under the condition of non-straw mulching in the paddy field. The number of preferential flow paths of both conditions are decreased by with increasing soil depth. But the number of preferential flow paths for paddy fields under the condition of straw mulching fell faster at the speed of 4.48 times. The average complexity of preferential flow paths under the condition of straw mulching is 2.11, while the average complexity of preferential flow paths is 2.14 in the paddy field under non-straw mulching conditions, and the difference between the two is significant (P < 0.05). In other words, the non-straw mulching preferential flow paths has a higher degree of distortion, which is reflected in the spatial distribution state of more concentrated path, and measures of straw mulching affect the preferential flow paths of paddy field. Although straw mulching accelerates the movement of soil surface water flow, the development of preferential flow paths in deep soil and the deep leakage of field water and fertilizer are reduced, which improves the utilization rate of water and fertilizer in crop ploughing layer to some extent