For the duct grouting of prestressed beams，due to the narrow passageways grouting，the paste in the flow condition is very complex. In order to understand the grouting body in flow，the article establishes a three dimension finite element model of the grouting body，and uses the fluid mechanics software Fluent to analyze the grouting process of the standard prestressed beams through the finite element numerical method for the first time. The results show in the speed of cloud，the paste which is in a straight space and passes top space flows slow，may cause grouting defects. In the cloud of duct static pressure，the static pressure in the centre of the duct is greater than those on both ends. When paste is in hydration process，secrete water is forced to flow to the two ends，which causes grouting defects. The analysis results provide theoretical and actual testing data processing support for grouting nondestructive testing technology.