The effects of the rice-duck-crayfish （CDR） model on soil fertility in paddy fields were studied by using field experiments and sampling tests from 2022 to 2023. The physical， chemical， and biological properties of soil after harvesting rice were compared between CDR and the rice monoculture （RM） model. The fertility of soil under two models was comprehensively evaluated by combining fuzzy comprehensive evaluation method and simple linear scoring method. The results showed that the content of microbial biomass nitrogen in soil significantly decreased by 53.27% after 2 years of CDR. The content of organic matter， total nitrogen， available potassium， and microbial biomass carbon in soil had an increasing trend， while the pH， the content of available nitrogen， available phosphorus， acid phosphatase， and alkaline phosphatase in soil had a decreasing trend， but there was no significant difference. All indexes except for the content of microbial biomass nitrogen had a decreasing trend to varying degrees compared with RM. There was no significant difference between CDR and RM in term of soil fertility. However， CDR had an upward trend in the soil fertility index of paddy fields， with an increase of 7.94%， while the soil fertility index of RM decreased， and the soil fertility index of CDR was 3.03% higher than that of RM in 2023. It is indicated that there was no significant change in soil fertility in paddy fields under two years of CDR.