Abstract: A gap and step prediction method based on digital measurement technology is proposed. The door-door frame assembly is taken as an example to illustrate the relevant algorithm and process. Firstly, the technical principle of photogrammetric-scanning measurement method is introduced. Then taking aircraft door assembly as an example, the procedures of measurement data analysis are introduced in detail from three aspects: constraint relation establishment, door position adjustment and gap/step calculation. Finally, an aircraft door is taken as the verification object to predict the value of the gap and step. At the end of article, the predicted value is compared with the measured value after assembly to verify the effectiveness and feasibility of this method.