This paper introduces a interpolation Preisach model. The first step in analysis of the model is calculating a maximum of eight conditions of the Preisach diagram at the points of divided fields, which are located on both sides of the actual field changed in direction. The condition of the Preisach diagram is separated into plus or minus values by a step-shaped interface due to past magnetic history. Next, the magnetization corresponding to the actual fields is linearly interpolated using previously calculated values. Magnetic field analysis with the model becomes possible in the case of occurrence of an optional reversal field. The model is used for simple magnetic field analysis of a magnetic sample ring. The model's validity is confirmed by agreement between the analytical results and actual measurements.