To support the refined management of water ecology in cold-region river basins and clarify the differential driving characteristics of water quality and antibiotics on microbial communities in winter and summer, as well as the concentration effect inflection points of key environmental factors, this paper focused on a typical cold-region river basin, integrated 132 valid samples (68 in summer and 64 in winter), and constructed an association dataset containing eight water quality indicators, 11 antibiotics, and microbial communities. This paper applied the Random Forest (RF) model to analyze the relationship between environmental factors and community diversity, combined SHapley Additive exPlanations (SHAP) interpretable analysis to identify key driving factors, their concentration effect inflection points, and multivariate interactions, and analyzed the seasonal differences in community function potential through Canonical Correspondence Analysis (CCA). The results indicate that the environmental and community characteristics of this cold-region river basin exhibit significant seasonal differences; the dissolved oxygen (DO, mean value of 10.32 mg/L) in winter is significantly higher than that in summer (6.95 mg/L); the mass concentration fluctuation of antibiotics such as norfloxacin (NOR, mean value of 156.76 ng/L) in summer is much higher than that in winter (1.23 ng/L), and the community diversity and functional potential show significant seasonal differences; TN is the key factor driving the changes in Shannon index in both winter and summer, while PD_whole_tree index is dominated by macrolide and tetracycline antibiotics in summer and by DO and quinolone antibiotics in winter, indicating that the driving factors of microbial community diversity exhibit seasonal specificity; SHAP analysis further identifies the potential concentration effect inflection points of key factors such as DO (7.41 mg/L in summer, 10.26 mg/L in winter), and TN (1.01 mg/L in winter), preliminarily revealing their concentration ranges that exert promoting or inhibitory effects on microbial community diversity; there are synergistic effects between multiple antibiotics and DO in summer and between TN and oxytetracycline (OTC) in winter, and the multi-factor combined pressures in complex environments have a superimposed impact on microbial communities; the community information storage and processing functions in winter are dominated by DO and temperature, while the cellular processes and metabolic functions in summer are regulated by multiple antibiotics, forming a seasonal differentiation pattern of "water quality dominance in winter and antibiotic regulation in summer". Methodologically, this paper integrated machine learning and interpretable analysis and revealed the seasonal response patterns of microbial communities to combined environmental pressures in cold-region river basins. The proposed concentration effect inflection points provide a scientific reference for the season-specific ecological risk management of river basins.