Abstract: The dry-wetting cycle is the primary factor causing the development and expansion of internal cracks in loess soils in Northwest China. Through indoor dry-wetting cycle tests, the quantitative characterization of cracks is conducted using the particle and crack analysis software (PCAS) to explore the influence of the dosage of biological polymers and the dry-wetting cycles on the morphological parameters of loess cracks. Combined with SEM tests, the mechanism by which biopolymers inhibit crack development was revealed. The research results indicate that at xanthan gum and guar gum dosages of 2.0% and 1.5% respectively, the crack rate of the modified loess decreases by 22.3% and 72.0%, and the water holding capacity increases by 43.4% and 15.7%, respectively. When the dosage of guar gum is 0.5%, the average crack width of the modified loess decreases by 55.8% compared to the plain loess. The mechanism by which biopolymers inhibit the development of fractures in loess mainly involves two aspects: On the one hand, through the bond energy strengthening of hydrophilic groups and the cementation-bridging effect, it effectively restricts the lateral deformation and longitudinal settlement of the soil; on the other hand, by filling pores and a film-forming water-blocking effect, it reduces the thickness of the hydration film of clay minerals and slows down the rapid formation of the water gradient within the soil. The findings are expected to provide a reference and insights for preventing loess engineering cracks in Northwest China and for loess improvement research.