CONTEXT: Deficit irrigation, brackish water irrigation, and biochar application are widely regarded as crucial technologies for conserving freshwater resources and protecting ecological environment in arid irrigation regions. However, the effects of existing management strategies on agroecosystem multifunctionality and their trade-offs remain insufficiently explored. OBJECTIVE: This study investigated the impacts of varying moisture, salinity, and biochar conditions on agroecosystem functions, services, and their interrelationships. It further explored potential trade-off mechanisms, providing a scientific basis for sustainable agroecosystem development. METHODS: A two-year field experiment was conducted in the arid region of Northwest China from 2020 to 2021. The experiment included eight treatments, which were designed as a factorial combination of three factors: two irrigation levels (full irrigation: W1; deficit irrigation: W2 = 1/2 W1), two water salinity levels (fresh water: S0 = 0.71 g L-1; brackish water: S1 = 4 g L-1), and two biochar application rates (B0: 0 t ha-1; B1: 60 t ha-1). RESULTS AND CONCLUSIONS: Compared to full irrigation treatments, although deficit irrigation significantly enhanced regulating service, it substantially reduced provisioning and economy services, thereby decreasing average multiple agroecosystem services by 28%. Full irrigation with brackish water alleviated the adverse effects of drought on provisioning and economy services, but it generally reduced the supporting, regulating, provisioning, and economy services, ultimately reducing multiple agroecosystem services compared to full irrigation with fresh water. Biochar application significantly enhanced regulating service while also providing certain benefits to supporting and provisioning services, but it significantly reduced economy services, finally leading to an increase of 3%-11% in multiple ecosystem services under appropriate water and salt conditions (W1S0, W1S1 and W2S0). Biochar application decreased the degree of trade-offs among services in most cases under full irrigation with both fresh and brackish water, indicating that biochar provided an ecological agriculture pattern by balancing productivity and environmental sustainability under well-watered conditions. SIGNIFICANCE: This study demonstrates that biochar application can enhance multiple agroecosystem services and reduce most of trade-offs among multiple services, which is crucial for sustainable agricultural development under special water and salt treatments.