As an ecofriendly and low-carbon binder, biopolymer has been used as the reinforcing material for stabilizing marine soils. However, the biopolymer-reinforced soils always show low resistance to moisture. Recent studies found that the carrageenan-reinforced calcareous silt may show some differences when facing the moisture-induced degradation. In this study, water immersion tests were performed on carrageenan-reinforced calcareous silt with different biopolymer dosages and dry-wet (DW) cycles. The specimen dimension, shear wave velocity, electrical conductivity, thermal conductivity, and UCS strength were measured for these specimens. The changes in the physical and mechanical properties of the reinforced soils with dry-wet cycle were studied. It is found that the total volume of specimen is decreasing with dry-wet cycle. Shear wave velocity, thermal conductivity, and unconfined compression strength (UCS) increase at DW = 1 and then drop continuously. The mass percentage of 3% carrageenan is considered as a better dosage compared with 5% carrageenan content with the balance of morphology and strength degradation. The microscopic images of the tested specimens show clear degradations of carrageenan bonds connecting soil grains. The belt form of the carrageenan is transferred to the silk form after a few dry-wet treatments.