Abstract: A special round reflector can be used in the Fizeau interfermeter system to achieve the one-time measurement of the cylindrical outer surfaces roughness. However, the relative spatial position of the reflector and the cylinder to be tested is difficult to accurately determine, so the measurement misalignment error will be introduced, which will affect the accuracy of the measurement results. In order to eliminate the errors, the types of errors and causes should be concretely analyzed. The light propagation path was studied, and the mathematical model was established. In cylindrical coordinate system, the relations of offset misalignment error, rotation misalignment error, processing angle error and measurement of the optical path difference were obtained. The Matlab software was used for simulation, and the interference fringes corresponding to the three kinds of misalignment errors were plotted. The interference fringes with errors introduced were analyzed, and the experimental results were compared to reduce the effect of error on measurement results. Finally, the morphology information of the cylindrical outer surfaces was obtained.