Objective: To investigate the associations between 24 hour activity and the quality of life (QoL) in children with autism spectrum disorder (ASD), and to explore their isotemporal substitution effects, providing a reference for developing intervention strategies of their QoL. Methods: From March to June 2025, 288 children with ASD from 7 special education schools in Jinan were selected by using a cluster random sampling method. The 24 hour activity was measured by using ActiGraph wGT3X-BT triaxial accelerometers, and their QoL was assessed by applying a parent proxy Pediatric Quality of Life Inventory. Multiple linear regression was employed to analyze the associations between 24 hour activity and QoL in children with ASD. Isotemporal substitution analysis was applied to analyze the dose response relationship of 24 hour activity time and the QoL scores in children with ASD. Results: Within the 24 hour activities of children with ASD, the daily time spent in sleep, sedentary behavior (SB), light physical activity (LPA), and moderate to vigorous physical activity (MVPA) were 610.49，605.80，195.49，28.22 minutes, respectively. Multiple linear regression analysis showed that, after controlling for confounding factors such as gender, age, and parental education level, the proportion of time spent in MVPA was positively associated with QoL scores ( β =1.75) in children with ASD, whereas the proportion of time spent in SB was negatively associated with QoL scores ( β =-1.00)(both P <0.01). In the dose response relationship, reallocating time from sleep, SB, and LPA to MVPA was associated with an improvement in QoL in children with ASD, with increased scores of 1.38, 1.55, 1.47, respectively; conversely, the reverse substitution was associated with a decline in QoL, and the scores decreased by 2.31, 2.99 and 2.68, respectively, with the latter demonstrating a more pronounced effect(all P <0.05). Conclusions Enhancing the QoL for children with ASD should be grounded in the overall balance of 24 hour activity. Time reallocation strategies should be implemented with an emphasis on relatively increasing MVPA and reducing SB.