Abstract: The standard three-dimensional model was applied to calculate the flow fields around one-segment and two-segment inspection robot in the horizontal straight pipelines.On the basis of some reasonable assumptions,the discrete of governing equations for in-pipe flow field around the robot were made with second order upwind scheme.The equations were solved with the SIMPLE algorithm.The obtained velocity and pressure field around one-segment and two-segment robot showed that the upstream flow field was relatively steady,and the force acted on the upstream end of the robot was simple.The pressure at the lateral surface of robot's body was ultra-negative.The more segments would result in a larger negative pressure.So the inspection unit should be located at the upstream side of the robot.The problem of cavity in fluid field should be taken into consideration during structure design of robot.