Research scholars believe that the characteristic values (d50,UC) of reservoir grain size is the design basis for sand control completion. Based on the relevance of gamma logging, density logging to the grain size characteristic values, we established the sample library of wells gamma, density log and grain size values. Using neural network technology, the learning network project was trained, then combined with logging data development block, the vertical profiles of entire reservoir grain size was established. This technology is very important to sand control completion for the reservoir lack of grain size data. It provides an accurate basis for project design and has a good application effect in the field.