To examine the pumping flow behavior of fresh concrete in vertical upward pumping， the flow of three concretes with different fluidities in a vertical pipeline was investigated by numerical simulation. The distribution of pressure and velocity field in concrete during pumping were analyzed in detail. The results show that the magnitude of pumping pressure is mainly affected by the properties of the lubrication layer. The longitudinal pressure distribution is related to the pattern of boundary resistance variations along the pipe wall， while the pressure at cross-section center is marginally higher than that at the pipe wall. Moreover， the research identified the flow behavior of concrete in the pipe， involving progression， diffusion， retention， accumulation， and convergence. Based on this， an analysis was conducted to understand the formation of the lubrication layer and the migration of coarse aggregates. These findings explained the reasons for concrete pumping segregation and plugging.