In the new media era ,the spread of rumors has changed a lot. Gordon W Allport and Leo Postman have developed the rumor propagation formula:Rumor=Importance×Ambiguous and subsequent researchers should further adjust the development of the formula with the times. Combined with the change of media environment and on the basis of previous studies, this paper puts forward a new rumor propagation formula:Rumor=Importance×Ambiguous×Transmitter Influence/Critical. The paper takes the new media era ——micro-blog as an example to make an empirical analysis of the text of the Sina micro-blog rumors about the incident of the northeast tiger tourist casualties in July 2016,and verifies the rumor propagation formula.