Artificial seismic source is a high precision method of measuring underground wave velocity changes at present. Large capacity airgun has unique advantages of appropriateness to detect and monitor the subsurface structure in land area scale. We selected the air-gun signal data since August 2013 of three seismic stations at Shihezi，Shichang and Wusu which are near the epicenters of two earthquakes with MS5.0 in Xinjiang. We studied travel time variety characteristics before the two earthquakes on the basis of the seismic phase of reflection wave and cross-correlation delay technology and achieved the preliminary results as follows: (1)It's reliable to select the seismic phase window with the single-double layer velocity model of the “3400 travel time table” and reference theory PmP. (2)Before the two earthquakes，the PmP travel time variety recorded by three seismic stations all have low abnormal process of value in different degree which lasts for 4 months and 2 months，and the range ability of relative travel time is about 0.1%to 0.26%，and the abnormal features in Shihezi and Shichang seismic stations are more obvious than Wusu seismic station which is farther from the epicenters. (3)There is difference in the change time of abnormal travel time and change range before two earthquakes with MS5.0，which may have relationship with the difference of magnitude degree and epicentral location.