The development of soil cracks endangers the stability of soil bund, further influences soil conservation. In order to reveal the law of crack development and the main influencing factors under water evaporation, a typical purple soil bund on sloping farmland in Beibei district of Chongqing was chosen to sample and test. Different levels of initial water contents (25%, 30%, 35%), dry densities (1.3, 1.4, 1.5 g/cm³) and reinforcements (0.05%, 0.15%, 0.25%) were defined to model the crack development process of purple soil bunds by using a set of simulated bunds. The crack development intensity, complexity indexes and the relationship between crack development and (initial) water content, dry density, and reinforcement were studied through image analysis. The results showed that the crack development process could be divided into three stages under water evaporation in terms of the initial stage, rapid crack expansion and stabilization. Under different initial water contents, the cracks intensity and complexity of all specimens increased rapidly with the decreasing water evaporation, and then tended to be stable at the water content of 12%. Dry density was an important factor impacting soil shrinkage and swell. Under the same initial water content, the cracks intensity and complexity increased as dry density increasing. The amount of reinforcement of polypropylene fiber was inversely proportional to the degree of cracks development. Comparatively, the initial water content had a great impact on the early stage of crack development in the process of water evaporation, but after the cracks began, the water content became a more important impacting factor, followed by the dry density and reinforcement. These results are expected to provide a basis for the design, construction, maintenance and management of soil bunds in purple soil area.