Collecting fixed stations and six ambulatory stations observational report of MinxianZhangxian MS 6.6 earthquake sequence,extracting travel-time information of P-wave and S-wave, using the multi-station method to compute wave velocity ratio of this earthquake sequence.The results show that there is a decreasing trend of velocity ratio before strong after-shocks.It is of reference value and indicative significance on the short-imminent term prediction of strong aftershocks. Although the wave velocity ratio anomaly is still a controversial issue,domestic and foreign scholars have made some achievements in theory and practice.In 1928,the Japanese seismologists Wadati Kiyoo first proposed the calculation method of wave velocity ratio:multi-station method.In 1962,the Soviet Union scholar Semionov published the first results of velocity abnormal in Garm region,found wave velocity anomaly and wave velocity ratio anomaly before earthquake magnitude greater than 3.5.In the early 1970s,Japan,the United States and other countries have also found a lot of wave velocity anomaly before earthquake.Especially American scholar Aggarwal found the change of wave velocity ratio anomaly before several small earthquake(the maximum magnitude is 3.3)in earthquake group and proposed to explain the anomalous with DD mode.At the same time,domestic scholars got some useful results in this field.In 1970s,Feng et al.summed up in the evolution of the crust,physical properties of medium will produce a series of changes,such as the emergence of micro fracture,expansion,seismic waves through the earth’s crust medium,and velocity will change accordingly,which is an important basis for the study of the wave velocity ratio of the medium.Wang et al.(2011)made a further research of variation characteristics of wave velocity ratio before and after the Wenchuan earthquake.Feng et al.(2009)studied the average wave velocity ratio in the northeastern margin of Qinghai-Tibetan Plateau,and found that there is a certain difference in the spatial distribution of wave velocity ratio.Li et al.(2006)found strong aftershock wave velocity ratio before trend decline.Based on the previous theoretical and the actual data,we conclude that the average wave velocity ratio of this sequence is 1.713,which is consistent with the results of Feng et al.(2009).It is a different levels of wave velocity ratio decline trend before the aftershocks with ML≥3.0occurred.Most of the aftershocks with ML≥3.0occurred in the process of the wave velocity ratio of sequence pick-up after down to the lowest,however,only a few aftershocks with ML≥3.0occurred while wave velocity ratio in the process of down to the lowest.