Abstract: A fluid analogy method (FAM ) is presented in this paper for estimating ODs of transit passenger in Bei-jing .It is based on the concept of pipe flow ,where transit route and passengers are modeled as the pipes and fluid and the OD matrix of a bus route is estimated based on passenger boarding-alighting counts .The accuracy of the OD matrix esti-mated based on the boarding-alighting data is tested against the observed OD matrix obtained from the transit IC card data over the segmented pricing routes in Beijing .It is found out that the estimation errors for the OD matrix at the AM peak , the PM peak and within the whole day are more than 0 .75 .Meanwhile ,the correlation coefficient between the actual dis-tance traveled and estimated at the AM peak hours ,the PM peak hours and within the whole day is 0 .98 ,0 .98 and 0 .99 respectively ,which supports that the proposed FAM method shows a good accuracy and reliability in estimating OD ma -trix of transit route .Compared with traditional equalization algorithms and other analytical models ,the proposed method is simple ,efficient and has a unique solution .Therefore ,it is believed that the proposed FAM method should be useful for public transportation agencies in their scheduling and dispatching routines .