A new U type flow meter was used to evaluate the rheological behavior of cement paste and mortar with high fluidity, and the experiment was mainly carried on the flow time of the mortar. By changing water cement ratio, the content of superplasticizer and the mass ratio of the aggregate to the paste, the validity, sensitivity and scope of this method were tested. A new method to evaluate rheological behavior of high fluidity cement paste and mortar is proposed in this paper.