  We introduce the cross spectrum based FRB (Fast Radio Burst) search method
for VLBI observation. This method optimizes the fringe fitting scheme in
geodetic VLBI data post processing, which fully utilizes the cross spectrum
fringe phase information and therefore maximizes the power of single pulse
signals. Working with cross spectrum greatly reduces the effect of radio
frequency interference (RFI) compared with using auto spectrum. Single pulse
detection confidence increases by cross identifying detections from multiple
baselines. By combining the power of multiple baselines, we may improve the
detection sensitivity. Our method is similar to that of coherent beam forming,
but without the computational expense to form a great number of beams to cover
the whole field of view of our telescopes. The data processing pipeline
designed for this method is easy to implement and parallelize, which can be
deployed in various kinds of VLBI observations. In particular, we point out
that VGOS observations are very suitable for FRB search.
