Abstract: An improved cloud motion wind height assignment algorithm with infrared window channel and water vapour absorption channel was proposed.Our algorithm separates tracers with cirrus clouds from the ones with lower level clouds.For tracers with cirrus clouds,both infrared and water vapour channels were used in height assignment;while for tracers with lower level clouds,only infrared channel was used.In case of cirrus cloud tracers,it is assumed that there is no any water vapour above cirrus cloud level.With this assumption,the original clouds should be observed by the satellite with same brightness temperature at both infrared and water vapour channels.Combine the above relationship with the statistic relationship between infrared and water vapour measurements,height assignment of semi-transmissive cirrus cloud was made.