Abstract：Specific surface condition in West China causes excessive velocity mis-tie at intersecting point of seismic lines to greatly reduce the accuracy of velocity field. Authors analyse the reasons why there occurs velocity mis-tie at each intersecting point of seismic lines. In velocity analysis，a seismic velocity curve may be divided into several segments，and velocity variations of corresponding segments are same at intersecting point of lines. Average velocity is nearly linear，and it may be approximated to a broken line. Each segment of the broken line corresponds to a formation. The time mis-tie corresponding to each segment is estimated and used in correction to achieve the velocity closure. Real application proves the method effectrue.
