Objective: To examine the associations between 24 hour movement behavior allocation patterns and physical fitness as well as serum high sensitivity C-reactive protein (hsCRP) levels among female college students, providing evidence for developing personalized health promotion strategies. Methods: In September 2025, 48 female college students aged 18-22 years were recruited from a comprehensive university from Shanghai. Continuous 24 hour movement behaviors were monitored using a triaxial accelerometer (ActiGraph GT3X+). Serum hsCRP levels were measured (≥1 000 ng/mL was log grade inflammation), and physical fitness indicators including upper limb muscle strength, vital capacity, and maximal oxygen consumption (VO 2max ) were assessed. Spearman rank correlation analysis was used to evaluate the correlation between variables. Compositional data analysis combined with multiple linear regression was employed to construct isotemporal substitution models, evaluating the effects of substituting 30 minutes of one behavior for another on hsCRP and VO 2max . Results: Female college students had the longest average daily sedentary behavior (SB) time (643.2±103.2)min, which was higher than sleep time (452.4±90.0)min, light physical activity (LPA) time (279.0±76.8)min and moderate to vigorous physical activity (MVPA) time (66.0±21.6)min. Correlation analysis revealed that vigorous physical activity (VPA) was positively correlated with hsCRP levels among female college students ( r=0.47, P <0.05). Substituting 30 minutes of MVPA with sleep, SB or LPA significantly reduced predicted hsCRP levels among female college students ( β = -0.90, -0.90, -0.73), replacing 30 minutes of sleep with MVPA significantly increased predicted VO 2max levels ( β =5.12) (all P <0.05). The low grade inflammation group exhibited longer durations of high intensity activity participation and higher mean values for height, body weight, and grip strength compared to the normal group ( t =2.17, 2.52, 2.21, all P <0.05). Within the normal inflammation group, MVPA was positively associated with VO 2max ( β =0.18), while sleep was negatively associated ( β =-0.07) (both P <0.05). In contrast, no statistically significant associations were observed between any activity behavior and VO 2max in the low grade inflammation group (all P >0.05). Conclusions MVPA exerts bidirectional effects on the health of female college students. While it enhances cardiorespiratory fitness, it may concurrently elevate chronic low grade inflammation levels. To maximize health benefits, intervention programs focused on increasing MVPA should also give full consideration to the importance of restorative sleep.