According　to　the　diversity　of　fluid　composition　and　the　complexity　of　flow　pattern　of　rainwater　ill　the　pipeline,　a　flow　velocity　measurement　method　based　on　cross-correlation　analysis　is　proposed,　reference　flow　filed　measurement　technique　in　Particle　Image　Velocimetry.　The　fast　algorithm　of　cross-correlation　analysis　is　studied.　Established　a　pipeline　rainwater　calibration　device　using　weir　slot.　The　results　show　that　extracting　all　average　speed　from　the　velocity　field　can　smooth　the　flow　variability　and　accurately　measure　the　average　velocity　of　rainwater.