Abstract: The control of the flow channel size of the jet fuel nozzle assembly is of great significance to the reliability and safety of the aircraft. The traditional method is to screen through indirect flow test, which is not only cost-effective but also inefficient. This paper presents a measurement method of flow channel offset of nozzle assembly based on CT volume data. Firstly, RSF (Region-Scalable Fitting) model was used to segment the flow channel area of nozzle CT volume data, and then the inner and outer contour surfaces of the flow channel wereextracted. Then, the circular equations of the inner and outer walls of the flow channel werecalculated by the least square fitting method, and the flow channel offset wasobtained according to the inner and outer center distances. The CT image of the standard nozzle sample wasmeasured. The results showed that the method can accurately extract the contour surface of the flow channel, and the uncertainty of measurement was 0. 010 4 mm. It hada certain engineering application value.