Objective: To explore the effects of different positions, epoch lengths and cut points of accelerometers on the measurement of sedentary behaviour (SB), light physical activity (LPA) and moderate vigorous physical activity (MVPA) in school aged children, so as to provide a reference for optimizing the criteria of accelerometers to measure SB and physical activity in school aged children. Methods: From May 2021 to September 2022, 110 school aged children aged 8-12 years old were convenient selected from a primary school in Hangzhou, and the accelerometers were worn on the waist, back, thigh, and wrist during the school time, and the collected data were transformed into six datasets with different epoch lengths (1, 5, 10, 15, 30, and 60 s) and compared using 4 common cut points developed by Puyau, Freedson, Evenson, and Pulsford (a total of 96 combinations) for classifying the percentages of time spent in SB, LPA, and MVPA. The effects of different positions, epoch lengths and cut points and their interactions on the assessment results were analyzed using a three way repeated measures ANOVA, and the variability of multiple comparisons between groups was analyzed using a Bonferroni post hoc test. Results: Except for the interaction of cut point × position × epoch on the percentage of time spent in SB and the main effect of epoch on he percentage of time spent in MVPA were not statistically significant ( F =0.66，1.18， P >0.05), the remaining main effects and interactions of the three factors on the assessment results were all statistically significant ( F =6.28-11 662.28， P <0.01). The differences between the results of different positions were statistically significant ( F =90.98-308.79, P <0.01). The percentages of time spent in SB and MVPA decreased with the increase of epoch lengths, while the percentage of time spent in LPA increased with the increase of epoch lengths ( F =16.54- 676.35 , P <0.01). The difference between the results using different cut points measurements was statistically significant ( F = 98.14- 976.40, P <0.01). Conclusions Accelerometer methodological factors including positions, epoch lengths and cut points will affect the estimates of SB and physical activity in school aged children. Therefore, it is recommended that future studies need to optimize the applicability of accelerometer analysis methods in school aged children, and the comparisons of results between studies need to be treated with caution.