Water scarcity and intense evaporation in arid regions create significant challenges for agricultural production, particularly in cotton cultivation. Although managed deficit irrigation and irrigation with magnetically treated water have shown positive results, their combined impact on soil oxygen (O2) dynamics and microbial metabolic activity to alleviate cotton water deficit remains unclear. A field experiment was conducted in the transitional zone between the Tianshan Mountains and Taklamakan Desert in 2023-2024, comparing three irrigation regimes (conventional, 10 % deficit, 20 % deficit) and two plastic film widths (standard 2.05 m, ultra-wide 4.40 m). Results showed that ultra-wide film mulching maintained more stable soil O2 levels (16.1 %) than standard film (18.9 %) under 10-20 % water deficit conditions. The ultra-wide film with 10 % water deficit demonstrated the highest microbial diversity by the second year, with significantly higher relative abundance of beneficial Actinobacteria (22.6 %) than standard film (17.8 %). Notably, ultra-wide film with 10 % water deficit achieved a 14.0 % higher seed cotton yield (7350 kg hm-2) compared to standard film, white increasing irrigation water use efficiency by 13 % (0.2 kg m- 3). Moderating effect analysis revealed that soil oxygen concentration significantly regulated the relationship between microbial community diversity and cotton growth. These findings indicate that ultra-wide film mulching effectively creates a more resilient soil system under moderate water deficit, offering a promising strategy for sustainable cotton production in water-scarce environments.