[Subjective] Elucidating the effects of soil erosion-deposition on the soil quality of slope farmland in Mollisol region of Northeast China is crucial for protecting black soil resource and maintaining its sustainable utilization. [Methods] This paper, selecting two sloping farmlands located at Keshan county, Heilongjiang province as the study site, utilized the ¹³⁷Cs tracer technique to estimate soil erosion rates and the minimum data set (MDS) method to calculate soil quality index (SQI) to analyze impacts erosion-deposition of sloping farmland on soil quality in typical thick-layer mollic regions. [Results] 1) The soil erosion-deposition rate of slope farmland in the study area ranges from -1563.2 to 7916.1 t/km2^/a, with an average erosion rate of 2669.0 t/km2^/a. The spatial distribution of soil erosion rate along the hillslopes was characterized by intensive erosion in the middle and lower slope segment, light-moderate erosion in the top and upper slope segment, deposition at the 50 m slope segment at the foot of the slope, and the most severe slope segment of soil erosion was distributed in 120-170 m slope length. 2) The soil quality evaluation indicators based on the MDS included soil clay, soil organic carbon (SOC), total phosphorus (TP), available nitrogen (AN), soil microbial biomass carbon (MBC) and β-1,4-glucosidase (BG). Moreover, there was a significant linear positive relationship between the MDS-SQI and SQI based on the full data set (p < 0.001), indicating that the MDS could replace the full data set and really reflected the soil quality regime of the slope farmland in the study area. 3) In the study area, there was a significantly negative correlation between SQI and soil erosion rates in the erosion sites (p < 0.01); while the SQI numerally increased with deposition rates without significant difference in the depositional sites. The SQI in the erosion sites reduced by 13.3% on average compared with that in the deposition sites; and the spatial distribution of the SQI along hillslopes was opposite to that of the soil erosion rates. [Conclusion] Soil erosion in the study area is the key driving force to soil quality degradation in sloping farmland.