Abstract：The side wall interference and disturbance reflection from the front end wall of the sealed chamber in an extremely low wind speed calibration facility in dynamic operation mode might have influence on the flow field inside the chamber, thus affecting the calibration accuracy. These wall effects are investigated through numerical simulation in this paper. The moving overlapping grid technique is used in solving the URANS equations simulating the flow field in the chamber to investigate the effects of side-wall interference and the disturbance wave reflection from the front (upstream) end wall on the interior flow field and calibration. The flow fields in the cases with and without side walls are computed，both the computed flow velocity contours and the x-direction velocities on the trajectory line of the top center point of the probe strut in the two cases are compared. For the front end wall reflection of the strut rod disturbance, the boundary conditions with and without front end wall are used respectively in computing the flow field in the chamber. The computed flow field velocity contours at several instants in the two cases, and the x-direction velocities of the two cases on the trajectory line of the top center point of the probe strut rod are compared respectively. The computed results show that both the wall effects caused by the selected chamber cross section size and the front end wall reflection of disturbance have negligible influence on calibration accuracy. The numerical simulation provides a valuable technical support to the design of the sealed chamber in the calibration facility.