Abstract: To determine the shut-in time after fracturing and improve the ultimate gas recovery of shale gas wells, the optimization method of shut-in time in shale gas wells based on the characteristics of fracturing flowback fluid was proposed. The deep shale in Luzhou area and the medium and deep shale in Weiyuan area were studied. First, the shut-in time in the lab scale was obtained by spontaneous imbibition experiment. After that, fracture width and characteristic length in the field scale were inverted by using fracturing flowback fluid salinity and flowback efficiency data. Finally, the shut-in time in the field scale was calculated according to the dimensionless time model of spontaneous imbibition. The results indicated that the shut-in time was not always in a positive correlation with that in the lab scale. It was affected by factors including imbibition rate, fracturing flowback fluid salinity, flowback efficiency, etc. The result provides a new idea for optimizing shut-in time after fracturing of shale gas wells.