With the recently development of electronic technology, the cased hole formation resistivity logging has been rapidly developed in order to discover the distribution of residual oil in the middle or late exploitation stage of the oilfields. The logging technology has many advantages that include the monitor of residual oil through casing, tapping potential of old well, the determination of submerged oil layer, and the production dynamic monitoring. They have all received quite good application effects. However, the effective signal during the acquisition process is in the level of nano-volt, the casing, measuring frequency, measured from the electrodes, cement mantle, and the heterogeneity of cased hole all will make measured signal distort, the cased hole resistivity data in the pre- processing must be corrected for these factors. Based on the logging information characteristics of the Russian ECOS-31-7, the filtering and interpolating methods for the original discrete data have been analyzed. Furthermore, the correction methods, such as the heterogeneity of casing, cement mantle, and cement quality, have been discussed. The processing results of the original data by means of actual casing measurements in the oilfield indicate that the method is feasible and effective.