Abstract: Background　Axial spondyloarthritis (axSpA) is characterized primarily by low back pain and restricted spinal mobility. Physical activity (PA) serves as one of the key interventions for improving disease outcomes. Objective　To analyze the association between objectively quantified PA intensity and mental health, quality of life, and overall disease status, and clarify the clinical significance of moderate-to-vigorous physical activity (MVPA). Methods　This cross-sectional study enrolled axSpA patients attending the outpatient and inpatient departments of Rheumatology and Immunology at the First Medical Center of PLA General Hospital from August 2024 to March 2025. PA was monitored for 7 days using the Huawei Band 7. Participants were stratified into "guideline-met" group (≥150 min/week of MVPA) and "guideline-unmet" group (＜150 min/week). Mental health was assessed using the self-rating depression scale (SDS), self-rating anxiety scale (SAS), multidimensional assessment of fatigue (MAF), and Pittsburgh sleep quality index (PSQI). Quality of life was evaluated using the Assessment of Spondyloarthropathy International Society Health Index (ASAS-HI). Disease status was assessed using the ankylosing spondylitis disease activity score (ASDAS), Bath ankylosing spondylitis disease activity index (BASDAI), Bath ankylosing spondylitis functional index (BASFI), and Bath ankylosing spondylitis metrology index (BASMI). Logistic regression analysis was used to examine the associations between PA and ASDAS, and between PA and ASAS-HI, respectively. A structural equation model (SEM) was constructed with weekly MVPA volume as the independent variable, ASDAS and BASFI as mediators, and SDS and SAS as dependent variables, adjusting for age, sex, and body mass index (BMI), so as to explore the mediating effects of ASDAS and BASFI on the association between PA and mental health. Results　A total of 166 axSpA patients were included, comprising 133 males (80.1%) with a median age of 35 (IQR: 29 - 40) years. The median daily MVPA was 19.4 (IQR: 11.6 - 30.2) min. Totally 75 patients (45.2%) met the PA guidelines, while 91 (54.8%) did not. Meeting PA guidelines was significantly associated with lower scores on SAS (P＜0.001), SDS (P＜0.001), MAF (P＜0.001), PSQI (P=0.019), ASAS-HI (P＜0.001), ASDAS (P=0.02), BASDAI (P=0.002), BASFI (P＜0.001), and BASMI (P=0.015). Multivariable logistic regression analysis revealed that MVPA was independently associated with disease activity scores (OR=0.96, P=0.002) and quality of life (OR=0.97, P=0.021). The revised structural equation model showed a good fit. Mediation analysis showed that the total mediating effect of ASDAS accounted for 35.4% (SAS) and 35.8% (SDS) of the total effect between MVPA volume and mental states, while the total mediating effect of BASFI accounted for 33.2% (SAS) and 32.8% (SDS). Conclusion　AxSpA patients achieve the recommended MVPA level (≥150 min/week) exhibit a healthier comprehensive mental status, higher quality of life, lower disease activity, and better functional status. Exercise prescriptions should be based on moderate-intensity physical activity (MPA) and supplemented by vigorous-intensity physical activity (VPA). Since controlling inflammation alone cannot fully address the psychological burden, incorporating functional status monitoring into the exercise intervention evaluation system is essential to further enhance the mental health benefits.