In coalfield geological logging work, it was often necessary to preprocess logging curves. In some well fields, due to the great difference of the coal strata resistivity curve amplitude, it was necessary to preprocess the resistivity logging curve in the result map output, so that the output of the logging result map was simple and beautiful, and the coal strata and marker layers were easy to identify. There were various preprocessing methods. The relatively traditional processing method was that the auxiliary curve was added or the resistivity curve was logarithmically calculated. However, there were some shortcomings in the practical application, resulting in the output of the logging map was neither simple and beautiful, nor could it highlight the key points, which brought inconvenience to the actual work. Using the 'open square method' to process the resistivity curve could solve the problems above and had certain advantages.