The variation characteristics of the load-unload response ratio with time before the Bao-tou M_S6.4 earthquake are studied by using the load-unload response ratio theory. The result showed that there is obvious anomaly before the earthquake. The influence factors on the anomaly contained not only time, amplitude, selected region and lower limit magnitude, but also seismotectonics and structures controlling earthquakes. For the relationship between anomaly and earthquake, there will be an earthquake when the ascendant anomaly has arisen, had a turn in the course of events and returned to normal. The time of anomaly is sustained from one year to four years.