The invention relates to a method and a device for reducing the running bearing temperature of a guide bearing of a water turbine. The method is characterized in that coolers matched with shapes of four external oil tanks are designed and attached onto the external oil tanks according to the shapes of the four external oil tanks of the guide bearing of the water turbine; guide pipes are respectively led from a main water supply thrust water supply pipe and a water drain pipe of a unit and enter a master loop pipe through a master water supply valve of the coolers; then after heat exchange of the coolers, heat is taken away by water of the coolers; and water enters a master water drain loop pipe, and is discharged to a thrust water drain pipe of the unit by a master water drain valve and discharged to a tail water outlet of the unit finally. According to the method and the device, the bearing temperature of the guide bearing of the water turbine can be reduced.