[Objective] The effects of rock fragment (RF) size and content on the development characteristics of surface shrinkage cracks in calcareous soil were studied to provide a reference basis for exploring the mechanism of soil erosion in karst areas.[Methods] RF size (2~5 and 5~12.5 mm) and RF content (0%, 10%, 20%, 30%, and 40%) were controlled, and digital-image-processing technology was used to study the effect of RFs on surface crack development in calcareous soil.[Results] ① The surface crack rate (SCR) of the calcareous soil without RFs was only 3.03%, whereas the samples with added RFs had a larger SCR. The maximum SCR of sample (5~12.5 mm, 40%) reached 8.66%. ② When RF content increased, the morphology of the crack network became small and dense, and small RFs made the crack network more complex. ③ The SCR of 5~12.5 mm RFs was positively correlated with the RF content, whereas the SCR of 2~5 mm RFs was negatively correlated with the RF content. ④ RFs can become the basis of fracture development, and each RF probably produce fracture around the RF or extend the crack network. Moreover, at the corner of an RF, it was easy to produce cracks extending outward.[Conclusion] The existence of RFs in calcareous soil could lead to the increase of the SCR and weaken the resistance of soil to erosion.